In the previous issue, we discussed the silenced P9S pistol developed for the U.S. Navy which featured an innovative stainless steel silencer developed at Qual-A-Tec and manufactured by Heckler & Koch GmbH. The Small Suppressor was designed to work with the MP5-N and MP5K-N submachine guns as well as the P9S pistol. The P9S pistol and Small Suppressor system became standard issue in the 1986, replacing the MK 3 suppressor and MK 3 MOD 0 pistol. The previous discussion detailed the design and manufacturing of the Small Suppressor and alluded to the Large Suppressor, which was developed when the Navy discovered that the otherwise outstanding aluminum silencer built in Germany for the MP5SD integrally silenced submachine gun was subject to severe saltwater corrosion. In this issue, we’ll wrap up the discussion of H&K’s Small Suppressor and conclude with a look at the Large Suppressor designed for the MP5SD-N integrally silenced submachine gun.

Both the Small Suppressors and Large Suppressors of Qual-A-Tec design were manufactured by H&K in house at Chantilly, Virginia, and subsequently at Sterling, VA. It is interesting that a German technician would always supervise a production run of suppressors to ensure quality control. The welding required for this design was particularly demanding, and the in-house reject rate (before reworking the bullet passage by line-boring a second time) was perhaps 20 percent until H&K built a special TIG (Tungsten Inert Gas) welder for fabricating the Qual-A-Tec designs. The reject rate immediately dropped to 1-3 percent (before reworking the bullet passage by line boring a second time).

While not required by the end-user, H&K always test fired each and every Small Suppressor on an MP5 with optical sight to ensure that the can delivered outstanding accuracy at 100 meters. One man would shoot one gun while another exchanged suppressors on a second gun, enabling them to test a lot of cans throughout the course of a night at the in-house range. Using almost any ammunition of the day, the MP5 with Small Suppressor would deliver 6-8 inch (15-20 cm) five-shot groups when fired in semiautomatic mode. Using Winchester 115-grain JHP ammunition, the Small Suppressor on an MP5 usually delivered 2-4 inch (5-10 cm) five-round group. A given gun would be more accurate with a suppressor than without, presumably because the weight of the suppressor dampened barrel harmonics. If the suppressor failed the accuracy test, redressing the bullet passage through the suppressor to remove any burrs usually corrected any accuracy problems. If that failed, it was destroyed. H&K delivered somewhere between 1,000 and 1,500 Small Suppressors to the U.S. Navy between 1986 and 1989.

The Small Suppressor we examined with a P9S pistol featuring standard fixed sights has the following markings: CAL. 9MM HK INC CHANTILLY VA SN 91 1156-1.

This particular weapon and suppressor were used for the testing of terminal ballistics during the Navy’s quest for an improved 9x19mm round for CT (counter-terrorist) missions. The mid- to late 1980s were an important time in the history of handgun ammunition. U.S. ammunition manufacturers competed in the development of improved handgun projectiles for law-enforcement applications. Simultaneously, U.S. military units with responsibility for in extremis missions (such as hostage rescue) sought projectiles that increased the likelihood of incapacitating the target, while reducing over-penetration which could place both hostages and rescue personnel at risk. Thus, the Small Suppressor was at the right place at the right time to provide the Navy with both a superior tactical tool as well as a handy research tool for the development of new ammunition.

H&K’s Large Suppressor

H&K began the development of an integrally suppressed version of the MP5 in the late 1960s. Herr Kästner developed this first variant of the MP5SD, which featured aggressive slot-shaped barrel ports designed to rapidly vent combustion gases into metal mesh, which was combined with a series of five baffles in front of the barrel. But the mesh fouled so quickly that it had to be replaced every 70 rounds and the slots significantly reduced barrel strength, so H&K began the quest for a more durable suppressor soon after this first variant of the MP5SD was produced in 1968.

Working from 1970 to June 1972, Walter Wolf subsequently developed a silencer featuring a coaxial design that employed aluminum square tubing for the inner coaxial structure and round aluminum tubing for the outer casing. The square tubing begins life as an aluminum extrusion, which is then machined so opposing sections on all four sides of the tubing, can be bent inward and welded to form four pairs of baffles. The machined cuts are designed so that one cut section is shorter than the section facing it, forming V-shaped baffles that point at the chamber. Since the facing legs of the V have different lengths, the bent sections of extruded tubing form asymmetrical surfaces for increasing the turbulence of combustion gases within the suppressor. Machined adapters are then welded in place at each end of the square module to center the module inside the outer tube. The net result is a coaxial design, with the inner coaxial chamber being square in cross section rather than circular. One adapter nestles in a channel cut in the dome’s front end cap, while the other is threaded to mate with the separate tube that surrounds the ported barrel. Once the adapters are welded in place, the square module assembly is bored for a bullet passage. The domed front end cap and rear end cap of the Wolf silencer are glued into place, so the suppressor must be submerged in a solvent such as Varsol for several days for periodic cleaning. Simply drain and blow out with compressed air.

The system is ingenious, well suited for mass production, and quiet. The patented Wolf silencer is 11.88 inches (30.2 cm) long and 1.58 inches (4.0 cm) in diameter. The aluminum silencer weighs 1.0 pounds (0.45 kg). When fitted with the aluminum silencer and retractable stock extended, the MP5SD3 is 30.4 inches (77.2 cm) long and it weighs 7.5 pounds (3.4 kg) empty and 8.7 pounds (3.9 kg) with a loaded 30-round magazine.

The Navy discovered that the aluminum components of the MP5SD suppressor were subject to saltwater corrosion. This stimulated Qual-A-Tec to develop a suppressor for the MP5SD that was fabricated entirely out of stainless steel. While heavier than the original factory silencer, Q’s stainless suppressor not only mitigated saltwater corrosion problems, it was also quieter than the Wolf design. Qual-A-Tec produced only a small number of these replacement suppressors before licensing the technology to Heckler & Koch. This design became the so-called Large Suppressor which H&K subsequently delivered to the Navy. Like its smaller sibling, the Large Suppressor also used Q’s Type 3 baffle.

The Large Suppressor is 12.40 inches (31.5 cm) long and 1.63 inches (4.14 cm) in diameter. The stainless steel silencer weighs 2.24 pounds (1.02 kg). Because the Large Suppressor had a greater diameter than the German can (due to using tubing of Imperial rather than metric measurements), H&K had to mill down the cocking lever supports on the MP5SD-N to provide clearance for the stainless suppressor when locking the cocking lever back in the detent.

The baffle stack of the Large Suppressor is about as long as the Small Suppressor, but the stainless steel replacement can for the MP5SD only incorporates six Type 3 baffles. This silencer features a domed front-end cap and a long primary expansion chamber. Designed to envelop the MP5SD’s ported barrel, the primary expansion chamber adds considerable length to the rear of the suppressor. This rear portion of the silencer is 4.75 inches (12.1 cm) long. The primary expansion chamber vents into a cylindrical coaxial expansion chamber via three rows of six large (0.50 inch, 1.3 cm) holes. A muzzle support separates the rear-most chambers from a secondary expansion chamber formed by a cylindrical spacer that fits tightly against the outer suppressor tube. Ports in the muzzle support enable gases from the chambers surrounding the barrel to continue forward through the suppressor, which prevents the buildup of back pressure from limiting the effectiveness of the primary expansion chamber and the coaxial chamber surrounding it. A cylindrical spacer separates the rearmost baffle from the muzzle support. Otherwise the design and function of the conical spacers is comparable to the Small Suppressor. The baffles have a larger diameter and, therefore, larger coaxial and annular expansion chambers to enhance the performance of the suppressor.

The Type 3 baffle used in the Large Suppressor is 1.19 inches (30.3 mm) long and has a diameter of 1.49 inches (37.7 mm). The cut-off chord is 0.78 inches (19.9 mm) long and has a maximum depth of 0.17-inch (4.4 mm) from the circumference of the rear baffle face. The rear face of the baffle has a diameter of 1.40 inches (35.6 mm) and the lip on the front of the conical spacer is 0.20 inch high with a wall thickness of 0.037-inch (0.94 mm). The LOA of the conical spacer and lip is 0.90 inch (22.9 mm). The bullet passage has a diameter of 0.39 inches (9.8 mm). The annular expansion chamber has a depth of 0.35 inch (8.9 mm) as measured from the diameter of the baffle’s front face, and the annular chamber has a length of 0.15 inch (3.8 mm). The three outlets venting from the annular expansion chamber into the slanted sidewall bullet passage have a diameter of 1/8-inch (3.2 mm). The slots in the rear face of the baffle are 1.0-inch (25.4-mm) long and 1/8 inch (3.2 mm) in width. An individual stainless steel baffle made for the Large Suppressor weighs 1.7 ounces (49 grams).

When fitted with the stainless steel Large Suppressor and folding stock extended, the MP5SD-N is 31.0 inches (78.7 cm) long, and it weighs 8.7 pounds (4.0 kg) empty and 9.9 pounds (4.5 kg) with a loaded 30-round magazine. Heckler & Koch made perhaps 750 Large Suppressors in Virginia, most of which went to the Navy between 1986 and 1989.

An interesting footnote to this story is that H&K still uses the extruded aluminum, square tubing silencer developed by Walter Wolf in the early 1970s as the standard issue sound suppressor on the MP5SD. A recently introduced, very simple modification to that design provides an impressive 3-decibel gain in sound reduction.

Conclusions

While the suppressed H&K P9S pistol was outstanding technology, the Teams seemed to prefer using a silenced submachine gun over a silenced 9mm pistol in the decade following the introduction of the Small Suppressor. Therefore, this silencer was normally fielded on an MP5-N or MP5K-N submachine gun. Despite the fact that the Navy adopted the .45 caliber Mark 23 Mod. 0 pistol from Heckler and Koch and the Model OHG suppressor from Knight’s Armament in 1996, the suppressed P9S pistol can still be found in the arms rooms of the Teams and are still available for missions. It is safe to say that the H&K P9S pistol with H&K’s Small Suppressor remains one of the best silenced 9x19mm pistols ever fielded by a military unit.

The stainless steel Large Suppressor designed for the MP5SD-N was about 19 ounces (0.55 kg) heavier than the aluminum factory silencer used in the MP5SD, but it provided the corrosion resistance necessary for amphibious operations in the marine environment. The Large Suppressor also provided superior sound reduction to the excellent German-made aluminum suppressor. While both the Large and Small Suppressors designed by Qual-A-Tec are now out of production, they represented a major improvement in the evolution of silencer technology when Heckler & Koch began producing them in 1986. Robust, accurate and quiet—these stainless steel sound suppressors fundamentally changed the subsequent direction of silencer design around the world. Heckler & Koch and Qual-A-Tec wrote a very important chapter of silencer history with their collaboration on the Large and Small Suppressors, and these outstanding sound suppressors remain in service to this day.

Author’s note: I would like to thank Frank W. James, Doug Olson, N.R. Parker, Hays Parks, and Jim Schatz for their considerable help with my research into this story.

Problem Solving With Low Signature Weapons: Part II

Hiding the Shooter

Using a suppressor to hide the location of the shooter is most commonly used by military snipers employing conventional (i.e., supersonic) ammunition. The suppressor thus enables the sniper to shoot more times (i.e., engage more targets) than might otherwise be prudent. Using a suppressor also dramatically reduces the risk from effective counter-sniper fire and improves the odds of a successful withdrawal from the enemy contact if circumstances warrant. Protection from counter-fire can also be an advantage in some law-enforcement scenarios, as well.

The suppressor hides the location of the shooter for three reasons.

(1) At typical engagement distances, most suppressors will lower the muzzle signature to less than the action noise of a self-loading rifle and less than the bullet flight noise. Thus, an individual who is downrange will attempt to locate the source of the sound not from the muzzle blast, but rather from the bullet flight noise. It is not uncommon for an individual downrange to turn his attention 45-180 degrees away from the shooter under such circumstances. I’ve experienced this phenomenon myself, both from the shooter’s position, and from an observer’s position as bullets fired from a silenced rifle passed close to my body while standing in the open. Both are dramatic experiences.

Generating this level of confusion by the use of a suppressor only works when the observer is within an arc of about 150 degrees in front of the shooter. Suppressors are less effective when observers are to either side of the shooter. Observers behind the shooter can locate the source of a suppressed shot from the direction of the sound as readily as if the shooter was using an unsuppressed rifle, as long as he or she can hear the ballistic crack. (Of course, if the observer can hear the muzzle blast or action noise from behind the shooter, then locating the source of the shot is easy.)

Using a suppressor with supersonic ammunition confuses downrange observers because the brain interprets the location of the sound to be perpendicular to the shock wave generated by the bullet. The amount of confusion is actually determined by three variables: bullet speed, distance between the observer and the shooter, and distance between the observer and the bullet flight path. Equations can be used to precisely calculate the amount of anticipated observer bias (the angle between the real and apparent location of the shooter) at a given temperature.

Another reason some individuals down range are confused as to the source of a suppressed gunshot is that the sound of the bullet strike draws their attention in the absence of a perceived muzzle signature. If bullet impact is behind them, for example, individuals between the shooter and the point of bullet impact may well turn their back to the shooter.

Furthermore, the advanced operator can position himself so that natural reflective surfaces (such as buildings, telephone poles, boulders and vehicles) will reflect the ballistic crack of a supersonic projectile away from the shooter, further enhancing the natural subterfuge generated by the wake produced by a supersonic bullet fired from a suppressed rifle. This skill takes some effort to develop, but it will become as natural as playing billiards, given enough practice.

Ironically, when using subsonic ammunition, an observer near the bullet flight path can frequently follow the “swishing” flight noise of the bullet back to the source of the shot. If a target is missed, he or she may have a pretty good idea where to shoot back, depending on such factors as environmental conditions and observer alertness.

(2) Using a suppressor also dramatically reduces the amount of energy available to disturb grass, leaves, twigs, and dust. This mitigates one of the greatest risks to the survival of a military sniper.

(3) While flash hiders can be quite effective at eliminating flash, which can be the most dramatic giveaway of a shooter’s position, they do nothing to tame recoil. And recoil compensators do not eliminate flash. All suppressors provide a substantial reduction of recoil, and properly designed suppressors dampen muzzle flash more effectively than flash hiders.

Thus a suppressor, combined with good field craft, can maximize the effectiveness and survivability of a sniper. One aspect of good field craft is rarely discussed, yet could easily negate the advantages of using a suppressor, relates to the ejection of brass.

The ejection of a spent cartridge case can catch sunlight and blaze for an instant like a camera flash. In Vietnam, U.S. snipers found that the flash of expended brass was one of the best tools for locating enemy shooters. This phenomenon is the main reason why most military snipers prefer manually operated, rather than semiautomatic, rifles. Admittedly, at least in theory, manually operated rifles should also be capable of better accuracy and reliability. When ejecting a case from a bolt-action rifle, the military operator should operate the bolt slowly and quietly until he can palm the empty case. Never leaving behind the spent cases (or food wrappers or other artifacts) has become a common operational theme among military snipers, so that the enemy cannot readily detect where the sniper’s hide was located. This makes tracking the sniper and anticipating future hide locations much more difficult. Getting back to the stealthy ejection of a spent case, it is desirable if circumstances permit to actually move the rifle under the operator’s body to help muffle the sound and to shield any possible glint from the brass case.

Law-enforcement snipers do not require the severe brass-management strategies now en vogue with military snipers. The simple expedient of draping a camouflaged cloth, frequently called a sniper veil, over the telescopic sight and back over the action and head. These cloths are generally large enough to fold on the ground to catch expended brass and shield any glint from escaping. The veil also helps shade the sniper from hot sun or shield the face and hands from cold wind. Fishing weights may be sewn into the corners of the cloth to keep it from fluttering on windy days.

While suppressor technology has matured dramatically in recent years, one aspect of stealthy shooting remains virtually ignored: the bright reflective finish of the brass cartridge case. Surely a manufacturer could develop a practical coating process that would give the case a non-reflective black finish. That would greatly facilitate the speed of follow-up shots and might also make semiautomatic rifles more practical for military sniping. Non-reflective black cases would certainly complement the use of a suppressor.

Although this attention to detailed field craft is highly relevant to the military operator, palming spent cases and some other aspects of military tactics vis-à-vis the employment of low-signature weapons are not really relevant to the law-enforcement officer. It should be emphasized that the mission of a military sniper is vastly different from a law-enforcement sharpshooter. A police marksman will attempt to get as close to the target as possible since placing a cold shot into a target’s CNS (central nervous system) is essential to instantaneously eliminate the subject’s ability to harm hostages or officers. Police shots will normally be less than 100 yards. A military sniper, on the other hand, will try to stay as far away from the target as possible to reduce the danger of effective counter-fire after he places a center-of-mass hit on a high-value target such as an officer, RTO operator, or personnel operating a crew-served weapon. Therefore, U.S. military snipers would prefer to take shots from a distance of 500-600 yards or more. Thus, bear in mind as this discussion continues that military and law-enforcement technologies do overlap—but missions, tactics and rules of engagement are commonly quite divergent.

The stealthiness of a suppressed gunshot has implications beyond strictly tactical considerations. Stealthiness also has what might be termed strategic implications; a properly employed low-signature weapon can prevent awkward to downright ugly problems with citizen sensibilities and headline-hungry news media.

Reducing Media-Relations and Public-Relations Problems

This area probably represents the single most useful—and the single most underutilized—application for silencer technology in the law-enforcement arena.

Outside of urban areas, common problems faced by law-enforcement officers include putting down an animal injured by traffic and responding to calls reporting a potentially rabid animal or a poisonous snake. One officer from southern Wisconsin recently had to deal with a crazed deer wreaking havoc inside a hardware store, another in Louisiana responded to a poisonous snake in a swimming pool, and an officer in Alaska had to dispatch a moose that tangled with a pickup truck. Using a duty sidearm or shotgun to put down an injured or potentially dangerous animal poses a potential public-relations nightmare if a small crowd has gathered or the animal is in a residential area. Most civilians are mightily upset by the noise of nearby gunfire, and their discomfort level is directly proportional to the intensity of the noise.

Perhaps the most useful tool for such problems is an integrally suppressed .22 rimfire pistol, although one should have previously consulted with a game biologist or veterinarian as to shot placement when dealing with anything larger than small game. This is particularly important when dealing with a potentially rabid animal, since its brain must be kept intact for analysis. Destroying the brain or allowing the animal to escape due to an improperly placed bullet would subject the victim of a bite wound to a grizzly series of anti-rabis shots.

Most silenced .22 pistols are built on the Ruger Mark II and feature a suppressor of the same diameter as the receiver. Thus most individuals will view this as a bull-barrel pistol even seen from an arm span or two. Furthermore, close observers who see such a firearm being used seem to conclude from the minimal noise generated by the pistol that some sort of low-power “humane” specialty ammunition was used. That’s especially useful if ultrasensitive environmentalists are encountered. Anyone inside a structure is unlikely to hear anything at all. I once fired a double tap from a suppressed Ruger pistol just outside of a frame structure three arm spans away from a woman washing dishes in her kitchen, and she didn’t hear a thing through the window that separated us.

A suppressed .22 pistol has several other interesting attributes. It can be kept unobtrusively in a small hardcase in the trunk of a squad until needed; a suppressed .22 rifle would tend to get in the way, present a higher profile when responding to a call, and might be more prone to damage in a squad’s trunk. The suppressed pistol can be carried in the case until ready to shoot. Simply evaluate the problem, make sure of a safe back stop, shoot as necessary, and dispose of the remains according to departmental policy. You should police up the fired cases as well. It’s amazing how discreet this process can be when the principal sound is the soft “thud, thud” of .22 caliber bullet impact.

Sometimes, however, a suppressed, bolt-action .22 rimfire rifle is the tool of choice. When employed with subsonic ammunition, this tool excels in two principal areas: (1) animal control in open areas such as airports and parks: and (2) the selective destruction of objects such as lights that create a problem for surveillance or entry teams. If one has the luxury of time, problem lights should be taken out a day or two prior to an operation—preferably while using a masking sound such as a loud motorcycle, garbage truck or helicopter flyby, as appropriate, to cover the tinkle of breaking glass and any possible ricochet. The use of masking sounds to hide a suppressed gunshot dates back at least as far as the Vietnam War. American suppressor designer Don Walsh, who spent considerable time in Indochina and now resides in Thailand, coined the term sonic camouflage for the practice.

Then there is the matter of media relations. The media seem to operate on the principal that “if it bleeds, it leads.” This problem is exacerbated by a general lack of understanding concerning the ethical and legal aspects of using lethal force. Furthermore, media personnel and lawyers also tend to have an appalling lack of understanding regarding firearms and ammunition. Using a .44 Magnum, for example, is likely to be perceived as excessive force. Yet, despite the fact that the .308 Winchester delivers three times more energy downrange, it seems much smaller to the eye and doesn’t have that nasty “M” word in its name. Thus it should come as no surprise that using a suppressed firearm reduces the perceived level of force by reducing the weapon’s noise.

Using a suppressed firearm also redirects media attention. If supersonic ammunition is used, the shot will appear to have originated near the point where the round struck. If subsonic ammunition is employed, the media may not even know when lethal force is used until other activity or a press briefing reveals that the situation has been resolved.

Beside providing a means to prevent PR problems, sound suppressors are useful for solving a variety of additional problems which will be examined in the conclusion to this discussion in the next issue of SAR. Specifically, we’ll explore the use of low-signature weapons to (1) enhance command and control; (2) preserve operator hearing, especially in confined spaces; (3) reduce the likelihood of detonation when operating in a potentially explosive atmosphere; (4) improve the quality and safety of live-fire training; (5) reduce muzzle blast and recoil; (6) safeguard human night vision and electronic night vision devices; (7) reduce the risk of so-called “friendly fire” accidents; (8) increase operational security, and (9) improve both practical accuracy and the speed of follow-up shots.

Problem Solving With Low Signature Weapons: Part I

Low-signature weapons are excellent tools for solving a remarkably wide array of tactical and public-relations problems. Yet relatively few law-enforcement agencies use low-signature weapons (LSWs) to their full potential. The practical employment of LSWs extends far beyond special-response units to marksmanship training cadre and, perhaps most of all, to the small-town or county officer for whom animal-control problems represent one of the most common call-outs. The following discussion explores eleven useful missions for low-signature weapons, which achieve their low sound signatures by the use of silencers, which have been more properly called sound suppressors since the mid-1960s. Some suppressors require specialty ammunition for optimum performance while others are designed to employ standard duty loads.

Throughout the century, the development of improved silencer technology has stimulated the evolution of tactical doctrine (as well as sporting applications), and the increasingly sophisticated tactical doctrine and sporting uses have in turn stimulated the further improvement of suppressor technology. A biologist would refer to this process as co-evolution. Armed professionals have learned that sound suppressors make effective tactical tools when employed for any of several reasons. Suppressors are typically used to either: (1) hide the fact that a shot has been fired; (2) hide the location of the shooter; (3) reduce public-relations and media-relations problems; (4) enhance command and control; (5) preserve operator hearing, especially in confined spaces; (6) reduce the likelihood of detonation when operating in a potentially explosive atmosphere; (7) improve the quality and safety of live-fire training; (8) reduce muzzle blast and recoil; (9) safeguard human night vision and electronic night vision devices; (10) reduce the risk of so-called “friendly fire” accidents; (11) increase operational security, and (12) improve both practical accuracy and the speed of follow-up shots. While a suppressed weapon may provide several of these functions simultaneously, the tactical user will commonly view one of these functions as the primary task of the suppressed system for a given mission. Some of the complexities involved with each of these applications are worth exploring in detail.

Hiding the Event

The uninitiated commonly believe that a silencer always hides the fact that a shot has been fired. While this effect can be achieved with the proper combination of weapon, cartridge and environmental circumstances, attaining this level of performance can be difficult. A suppressed firearm is generally used to hide the fact that a shot has been fired for one of three reasons.

(1) In the military environment, hiding the fact that a shot has been fired is essential for quietly eliminating a sentry, point man or other hostile without alerting nearby individuals. In the law-enforcement environment, officers face an increasing incidence of hostage situations. When that involves quietly dealing with multiple armed suspects in a large building, the risk level increases dramatically. The ability to quietly remove one threat without alarming other armed suspects can save lives.

(2) Both law-enforcement and military operations also may need to quietly eliminate a guard dog. While the 9x19mm round from the H&K MP5 SD has not proved to be effective in this role, an MP5 chambered in .40 S&W and employed with a good muzzle can holds more promise. Some departments prefer an integrally suppressed Marlin Camp Carbine in .45 ACP from companies like John’s Guns or SIOPTS for this role. Finally, the new Ruger Model 96/44 lever-action rifle and the Ruger Model 77/44 bolt-action rifle, fitted with a Dark Star suppressor from Sound Technology and employing heavy .44 Special rounds, provide effective tools for dispatching animals as large as deer.

(3) An increasingly common law-enforcement requirement is to quietly destroy selected objects (such as vehicle tires or yard lights) prior to a dynamic entry or pursuant to another tactical operation. Unless there is considerable environmental noise (such as a helicopter overhead in the law-enforcement realm or a nearby firefight in the military realm), hiding the fact that a shot has been fired generally requires the use of subsonic ammunition to avoid the loud ballistic crack that would be generated by a supersonic projectile.

It is important to understand that the use of subsonic ammunition limits the effective range of a weapon. If the suppressed firearm employs subsonic ammunition with a poor ballistic co-efficient (such as the 9x19mm and .45 ACP pistol cartridges), then the system could have a maximum effective range on the order of 100 yards (91 m). If the subsonic weapon employs ammunition with a good ballistic coefficient (such as the 7.62x39mm and 7.62x51mm NATO subsonic rifle cartridges), then the system could have a maximum effective range on the order of 200 yards (183 m). The outstanding 300 Whisper cartridge developed by J.D. Jones for SSK Industries can deliver 1 MOA accuracy at 200 yards in the proper suppressed weapon. The 53 grain 5.56x45mm Ultra Stealth subsonic round from Engel Ballistic Research will deliver 1 MOA from a 1 in 9 barrel at 87 yards (80 m), while Engel’s 220 grain 7.62x51mm Thumper subsonic rounds will deliver 2 MOA at 87 yards (80 m) with a 1 in 12 barrel. Both will defeat Level III-A body armor. Bullet flight noise produced by these subsonic rifle cartridges is less than the sound produced by an arrow in flight. The dominant sound with a well-designed suppressor then becomes bullet impact.

In practice, placing accurate hits at random distances out to 200 yards with a subsonic rifle cartridge is very difficult. Two factors create most of the problems: the rifling’s rate of twist, and range estimation. While current laser range-finding binoculars solve the latter problem, finding a source for barrels of the proper twist rate can be a challenge.

A fast rate of twist is typically needed to stabilize a subsonic projectile of conventional weight, although a new 7.62x51mm subsonic round developed by Black Hills may provide acceptable accuracy out to 100 yards using rifles with a 1 in 12 twist (like the Remington PSS) and good accuracy with a 1 in 10 twist (like the Savage Model 110FP “Tactical Rifle”). But that’s not universally true. Several superb custom rifles with barrel lengths of 20, 24, and 27 inches (51, 61, and 69 cm), featuring either polygonal or cut rifling, would barely place five shots on a sheet of 8.5×11 inch (22×28 cm) paper. Some shots were very high and some were very low, suggesting irregular ignition (a common problem with small powder charges in large-volume cases). Shooting on a hot, dry day at an altitude of about 1,500 feet (457 meters), only 20 percent of the Black Hills rounds remained subsonic in the three aforementioned custom rifles.

The Sound Technology subsonic round, on the other hand, delivered better than 0.5 MOA groups in the Savage Tactical rifle with Sound Technology Dark Star suppressor and the barrel shortened to 20 inches (51 cm).

Depending primarily on bullet length, some 5.56x45mm subsonic rounds are accurate to 80-90 yards with a 1 in 9 twist, while the SIOPTS subsonic rounds featuring ultra-heavy frangible tungsten projectiles require a 1 in 7 twist and a Colt milspec (as opposed to aftermarket or match) chamber and then provide excellent accuracy to at least 100 yards. I’ve not had the time to determine the SIOPTS round’s accuracy at 150 and 200 yards at the time of this writing; this may well prove to be a 200 yard cartridge.

Many subsonic cartridges employ a heavier than normal bullet to improve both external and terminal ballistics (which translate into improved shot placement and better stopping power). Using a heavier bullet may require such a fast rate of twist that appropriate barrels are extremely difficult to obtain, even from custom barrel makers. A further complication is that such a fast-twist barrel probably won’t provide acceptable performance with conventional supersonic ammunition, so it is generally necessary to dedicate a rifle to a subsonic cartridge. This is a good idea anyway, since a subsonic 7.62x51mm subsonic round will strike 4 to 14 inches lower than Federal .308M ammunition at 100 yards, depending on the design of the subsonic ammunition. Few centerfire rifles will perform well with both supersonic and subsonic ammunition. The most notable exception is the Savage Model 110FP Tactical Rifle with Sound Technology’s Dark Star sound suppressor and Choate’s Ultimate Sniper Stock. These three components together form a suppressed rifle system that provides superb sound reduction, 1/2 MOA accuracy with Federal .308M supersonic ammo and 1/4 MOA accuracy with Sound Technology subsonic loads.

The ability to instantaneously tell subsonic from supersonic ammunition becomes crucial if both subsonic and supersonic rounds may be used in the same rifle. European manufacturers tend to put a blue tip on the bullet of subsonic rounds, and at least one uses a blue case head. Subsonic 5.56x45mm and 7.62x51mm rounds from Engel Ballistic Research feature a white tip. And subsonic rifle rounds from Black Hills feature nickel-plated cases. Some individuals use a needle file to add small serrations to the rims of subsonic cartridges to facilitate identification during night operations, although a simpler approach is to always keep the subsonic ammunition in a particular pocket, pouch, or magazine of different capacity or construction.

Range estimation is critical when using a suppressed rifle with subsonic cartridge at long range, even if the projectile has a good ballistic coefficient. The 7.62×51 NATO subsonic round, for example, produces a bullet drop of about 3 feet (0.9 meter) between 100 and 200 yards.

It is also important to note that a rifle fitted with a muzzle can should always be fired with the can installed, since the weight of the suppressor plus the amount of torque used to install the suppressor both affect the point of impact. The zero will generally shift 2 to 12 MOA depending on the length and weight of the suppressor, the mounting method of the suppressor, and the rigidity of the barrel. Group size, however, will generally improve slightly when a well-designed suppressor is installed properly (compared to the same barrel as it came from the factory). The only exceptions in my experience involved installing suppressors of conventional weight on rifles with long, thin barrels. Adding a suppressor to a Steyr AUG with 20-inch barrel, for example, seems to exaggerate barrel harmonics and degrade accuracy to an unacceptable level. Short-barreled AUGs do not suffer accuracy problems when a suppressor is fitted, however.

Finally, it should be noted that the psychological impact of seeing an officer armed with a suppressed weapon can work for or against the armed professional, depending on the circumstances. For example, armed suspects confronted by officers of a special-response team employing suppressed weapons are likely to perceive a greater threat level from the officers and therefore may be less likely to respond with lethal force. The flip side of that psychological coin is that some knee-jerk elements of society view suppressors as sinister technology despite overwhelming evidence to the contrary. Clearly, the thousands of civilians who legally own silencers in the United States represent an impeccably responsible and law-abiding segment of society. Furthermore, a law-enforcement officer employing a suppressor is likely to perform his duties in a more professional manner, since that officer is probably better trained and better motivated, and the suppressor itself provides additional operational alternatives. But the aforementioned knee-jerk phobia regarding suppressors common to media personnel and some civilians may work against the officer’s best interests. Therefore, it would be useful to consider several strategies for avoiding problems in the media and in the courts following an operation using a suppressed precision rifle.

The first strategy is to keep the suppressed rifle cased or in a drag bag while deploying to the shooting position or hide. The second involves what should be a penetrating glimpse into the obvious: the marksman must practice regularly with the suppressed rifle and document his maintenance of that proficiency. This process has both tactical and legal implications. Clearly, any deficiencies in the marksman’s skill level or in the performance of the suppressed rifle must be determined on the practice range and not on a deployment.

Then there is the potential danger of civil liability, which can be minimized by basic attention to detail during training exercises. Cut out the portion of the target containing the first cold shot of the day, initial and date it, and tape into the marksman’s log book. In aggregate, the log book with its actual targets will provide a powerful tool for demonstrating an officer’s expertise in the courtroom, should that ever be required.

Assuming that a suppressed firearm and its cartridge deliver sufficient accuracy and adequate terminal ballistics, it is also important to realize that the muzzle signature is only part of the story when evaluating a system for tactical employment. Two other events are involved with a suppressed gunshot which can influence the stealthiness of that shot: bullet flight noise and bullet impact.

For example, when using a .22 rimfire rifle with a muzzle suppressor for the selective destruction of objects, it is important to realize that the muzzle can will not eliminate the ballistic crack produced by high velocity and sometimes produced by standard velocity loads. The subjective impression is that the ballistic crack is as loud as an unsuppressed .22 rifle, so subsonic Long Rifles or CB Longs should normally be used for the selective destruction of objects to keep the event from sounding like a gunshot. With the resultant dramatic reduction of the weapon signature and bullet flight noise, bullet impact becomes the dominant sound of the gunshot.

When employing a suppressed centerfire rifle with conventional ammunition, for example, the bullet impact in flesh is a loud and distinctive “pukk!” If the target is engaged over an open area with little ambient (environmental) noise, bullet impact can be heard clearly for hundreds of meters. When using a suppressed rimfire rifle or when using a suppressed centerfire rifle with subsonic cartridge, the sound of bullet impact in flesh is considerably less, but it’s still distinctive. When using a subsonic rimfire round on a tire, the muzzle signature might be undetectable to an observer 33 yards (30 m) away around the corner of a house, while the bullet impact may or may not be heard as a hollow thump. When using a CB Long to break a light bulb outside a frame house, the only thing a close observer might notice is the sound of breaking glass, while occupants of the house might hear nothing. The metallic ring of a hit from a CB Long on a tire rim, however, might be quite noticeable to the house occupants.

Merely using a quality suppressed firearm does not provide a carte blanche for the operator. Some other variables that will also affect the stealthiness of a suppressed gunshot include such things as ammunition, ambient noise, location of potential hostiles relative to the target, composition of target, composition of material behind the target, presence or absence of reflective materials (such as pavement or brick walls), presence or absence of absorptive materials (such as grass, bushes and trees), and shot placement.

A final footnote to hiding the event relates to the employment of suppressors with supersonic projectiles at very close range. Entry teams are increasingly using suppressed carbines of rifle caliber (commonly the Colt M4 with a compact suppressor such as the Gemtech M4-96D, Raider from AWC Systems technology, or titanium cans from SIOPTS or the Spec Op’s Shop) because of the weapon’s superior terminal ballistics compared to a submachine gun and because the 5.56x41mm cartridge will defeat most body armor. Armed confrontations in this environment tend to be up close and personal, and a suppressed weapon may be fired at a target which is so close that the supersonic projectile does not travel far enough to generate a ballistic crack. In such cases, the dominant sounds become the suppressed muzzle blast and the sound of bullet impact. Given ideal environmental conditions and a very short engagement distance, plus an excellent muzzle can, suppressed weapons with supersonic ammunition can be very stealthy. This phenomenon has been largely ignored by professional operators, but it might provide an interesting option given the right tactical scenario.

It is much easier to hide the location of the shooter than to hide the fact that a shot has been fired. While particularly valuable for military operators, this phenomenon can also be useful for law-enforcement applications as well.

The titanium Genesis family of sound suppressors from the Special Op’s Shop, Inc. were the first muzzle cans designed for the H&K MP5 submachine gun using a spring-loaded snap-on mount system. The example used for the following study has been intensively used and abused for four years, and it is still going strong. The Genesis suppressors represented innovative and robust technology when they were introduced in 1993, and they remain compelling and competitive technology today.

The Special Op’s Shop was established in 1982 by Chuck Good-rich to manufacture pistol and special
purpose ammunition, and the business broadened quickly to encompass a wide range of tactical gear and law-enforcement products. The company began manufacturing sound suppressors with the introduction of a muzzle can which featured a snap-on mount that wrapped around the front sight of an unmodified Ruger Mark II pistol with bull barrel. The line of snap-on submachine gun suppressors began as a collaboration between Tony Marfione and Jim Faranelli of B&B Guns in Hudson, Florida. They were having some problems with both design and manufacturing, so they contacted Goodrich for help. Those improved designs became the foundation for the current product line, and they moved all manufacturing to the Special Op’s Shop in Tennessee. Today, Chuck Goodrich offers a full spectrum of titanium and stainless steel suppressors and integrally suppressed weapons (Special Op’s Shop, Inc, P.O. Box 978, Madisonville, TN 37354; phone 423-442-7180; fax 423-442-6218; URL www.mindspring.com/~opshop/weapons.html). One of the most interesting products to my biases is the new titanium Viper suppressor, which attaches onto a standard AR15/M16 flash hider with a newly patented quick coupler. The most interesting new product under development is a snap-on .308 suppressor, which is slated for introduction in the spring of 1998.

The Genesis family of quick mount suppressors for the MP5 are designed to meet the most diverse operational requirements, and two thread-mount variants are also available for other 9x19mm submachine guns. Some variants are manufactured from titanium while others are made from stainless steel. Any suppressor is available in either a nonreflective bead blast or matte black finish.

The Genesis Model 3005 is a sealed unit fabricated from stainless steel, measuring 9.5 inches (24.1 cm) long and 1.48 inches (3.8 cm) in diameter. The can weighs 24 ounces (680 grams). The unit features Spec Op’s spring-loaded quick mount which allows installing the suppressor onto the three-lug barrel of an MP5.

The mounting process is quite simple. Begin by clearing the weapon. Then simply slip the can over the barrel and push the suppressor toward the receiver until the spring is fully compressed; now twist the suppressor 1/3 turn in a clockwise direction. The spring forces a notched collar forward to capture the barrel lugs and keep the suppressor in place despite intense full-auto fire that could cause a thread-mount suppressor to loosen. The operating spring in the quick mount is very stiff and requires considerable force to compress, so this is a very robust mounting system. Try to pull the suppressor off the barrel and try to twist the can back and forth to ensure than the can is securely fastened. While this is a useful procedure with any quick-mount system, it is particularly important with this system because the mount can be rotated too far (i.e., past the capture notches in the mount). Simply compress the mount spring and try again if proper alignment of the barrel lugs and mount notches has not been achieved. In practice, the mounting/dismounting procedure takes about five seconds.

The Genesis Model 3006 is the same size as the Model 3006, except that it is fabricated from titanium. The weight, therefore, is just 18 ounces (510 grams) including the snap-on mount. Six ounces lighter than its stainless steel sibling, the Model 3006 is also slightly more expensive because of the titanium. Both the Model 3005 and 3006 are designed for applications requiring the maximum possible sound reduction.

A smaller unit is also available for those missions where size is a paramount concern. Well suited for entry teams and the realm of Close Quarter Battle, the Model 3007 is also called the Genesis Tactical Entry Model. I personally like this concept very much. The titanium unit is 7.5 inches (19.1 cm) long and 1.48 inches in diameter, and the can weighs 16 ounces (454 grams) with snap-on mount.

My favorite variant of the Genesis series is the lightest of them all. Weighing just 11.6 ounces (329 grams) with snap-on mount, the Model 3008 is also called the Genesis Elite. The titanium suppressor has a length of 9.5 inches (24.1 cm) but a diameter of only 1.24 inches (3.1 cm). The relatively small diameter of this suppressor has definite advantages when used with some accessories designed for the MP5. While the robust snap-on coupler is standard issue on the Genesis Elite, the suppressor can also be ordered with a cam-lock coupler so the unit will not turn too far when installing the can on a weapon.

The Special Op’s Shop also offers two thread-mount suppressors that can be provided with the following thread pitches: 1/2×28, 1/2×32, 1/2×36, and 9/16×24 TPI. Similar in internal design to the Model 3005, the stainless steel Model 3009 is 8.5 inches (21.6 cm) long and has a diameter of 1.48 inches (3.8 cm). It weighs 20 ounces (567 grams). The titanium variant of this can is the Model 3010, which has the same dimensions but weighs 16 ounces (454 grams).

The particular specimen of the Genesis Elite evaluated in this study shows no signs of wear after more than 15,000 +P rounds. It features 17 closely spaced titanium baffles which show no signs of erosion. The snap-on mount spring remains strong and the suppressor still attaches as well to a three-lug MP5 barrel as it did when new. The suppressor tube features a generously knurled surface to facilitate mounting and dismounting the can; this eminently practical if luxurious feature has all but disappeared in the marketplace, and I applaud its incorporation into the Genesis Elite’s design.

Performance

Suppressor performance was determined by measuring sound signatures using the equipment and procedures specified at the end of Chapter 5 in the book Silencer History and Performance ($55 postpaid, Wideworld, Dept. SAR, P.O. Box 1827, Conway, AR 72033). The microphone was placed 1.00 meter to the left of the suppressor or muzzle according to U.S. Army testing procedures specified in MIL-STD-1474C. The ambient temperature during the testing was 79°F (26°C), and the speed of sound was 1,138 fps (347 mps). Velocities were measured in feet per second using a P.A.C.T. MKIV timer/chronograph with MKV skyscreens set 24.0 inches apart and the start screen 8.0 feet from the muzzle (P.A.C.T., Dept. SAR, P.O. Box 531525, Grand Prairie, TX 75053, 214-641-0049). At least 10 rounds were fired to obtain an average sound signature or muzzle velocity.

Testing employed a +P subsonic round featuring a 147 grain (9.6 gram) Hornady hollow point in front of 3.7 grains of VihtaVuori Oy N-320 powder. This load is specifically tailored to remain subsonic in the MP5 submachine gun. Most commercial 9×19 subsonic rounds are designed for pistols and, therefore, are frequently transonic or supersonic in the MP5. On the day of the testing, this round produced a muzzle velocity of 958 fps (292 mps) in the unsuppressed MP5 and 967 fps (295 mps) with the Genesis Elite fitted on the submachine gun. These velocities are not significantly different statistically speaking.

The unsuppressed H&K MP5 produced a sound pressure level (SPL) of 155 dB. When fitted with the Genesis Elite, the suppressed sound signature was 130 dB, for a net sound reduction of 25 dB. First-round pop with the suppressor installed was a modest +3.5 decibels.

Since this suppressor had 15,000-rounds worth of baked-on carbon which formed a thin veneer on the can’s internal surfaces, I was curious if the carbon affected system performance. Antares Technologies, Inc. provided sound test data on a new Genesis Elite using testing equipment and procedures also conforming to U.S. Army testing protocols specified in MIL-STD-1474C. This testing used 147 grain FMJ subsonic ammunition loaded with 3.8 grains of WW231 powder, and was conducted at 34°F (1°C). The speed of sound during this phase of testing was 1,138 fps (347 mps). Several contemporary suppressor designs from the Automatic Weapons Company of Boise, Idaho, were tested in addition to the Genesis Elite: the MK-9K and the MINITAC. The former is 8.0 inches (20.3 cm) long, 2.0 inches (5.1 cm) in diameter, and weighs 19.0 ounces (537 grams). The latter is 8.5 inches (21.6 cm) long, 1.38 inches (3.5 cm) in diameter, and weighs 10.3 ounces (292 grams). The comparative results of the sound testing are shown in Tables 1 and 2.

Since the different ammunition used during the two test days produced different unsuppressed sound signatures, the net sound reductions in Table 2 provide a better way to compare the various suppressors than simply using the actual sound pressure levels shown in Table 1. The Genesis Elite produced a net sound reduction of 30 dB on both days, suggesting that 15,000 rounds-worth of carbon buildup does not degrade the efficiency of this suppressor. While the MK-9K is 4 dB quieter than the Genesis Elite, the former has twice the volume and twice the weight of the Genesis Elite. The MINITAC has a similar volume and weight to the Genesis Elite, but the former has a larger diameter and a much greater first-round pop. Based on earlier unpublished data, the Genesis Elite is also quieter than the contemporary TAC-NINE suppressor, which was designed by Doug Olson for AWC Systems Technology and remains one of my favorite submachine gun cans of all time. Clearly, the Genesis Elite belongs on that list of favorites as well.

The Genesis Elite with snap-on mount from the Special Op’s Shop provides plenty of sound suppression for maintaining command and control and for safeguarding the operator from TTS and PTS (temporary and permanent threshold shift; i.e., hearing loss) during dynamic entries and Close Quarter Battle. Furthermore, this level of sound suppression is enough to hide the fact that a shot has been fired when employing subsonic ammunition in many real-world situations. The diminutive Genesis Elite produced a sound signature that was within 3 dB of a factory original MP5 SD integrally suppressed submachine gun. That’s impressive performance from such a small, light suppressor. The titanium Genesis Elite is a quiet, robust suppressor with an unusually secure snap-on mount that together make a suitable system for both the armed professional and the discriminating collector. The Genesis Elite is a world-class performer.

AWC Thundertrap .30 Caliber Suppressor

The .30 caliber Thundertrap suppressor from AWC Systems Technology represents a fundamental change in technology that forced me to reevaluate my biases regarding suppressor design for sniper rifles. I’ve long preferred two-point mounts for centerfire rifles for several reasons: (1) they tend to be quieter since they feature a large primary expansion chamber which extends back over the barrel; (2) they tend to be less prone to loosening during prolonged shooting sessions; (3) they tend to provide better accuracy at long range, presumably because they are better at dampening barrel harmonics; and finally (4) they have the potential to provide better alignment with the bores of premium barrels that have excellent concentricity. Nevertheless, the Thundertrap created something of an epiphany for me, and I am now a fan of the single-point mount as manifested by the Thundertrap suppressor from AWC Systems Technology. The virtues of the Thundertrap are manifest: it is half the size of many .30 caliber suppressors with two-point mounts, it provides a very pleasing sound signature, and it provides superior accuracy to an unsuppressed heavy barrel rifle at 600 yards (549 meters). The Thundertrap is an excellent choice for both the armed professional and the serious sportsman.

AWC fabricated the Thundertrap entirely from 304 stainless steel, which is rather unusual in the industry. Manufacturers of stainless steel suppressors commonly use 304 stainless for the tube and 303 bar stock for the other components, because 303 stainless is easier to machine than 304. AWC Systems Technology uses 304 series bar stock because it takes a superior weld. All internal components of the Thundertrap suppressor are welded into place, making this a very robust system. The Thundertrap is 8.5 inches (21.5 cm) long and 1.6 inches (4.0 cm) in diameter. The suppressor evaluated in this study weighs 33.6 ounces (2.1 pounds; 953 grams). While the Thundertrap is commonly used on rifles chambered in .308 Winchester (7.62x51mm), the suppressor also performs well on rifles chambered in .300 Winchester Magnum (no international nomenclature). The suppressor is finished in a matte black powdercoat. Thread pitch of the mount is commonly 9/16×24 TPI, but other threading is available when appropriate.

Remarkably, the internal construction of the Thundertrap is reminiscent of the .22 rimfire Backdraft suppressor also made by AWC. A given baffle technology rarely works well for both low-velocity and high-velocity combustion gases; this represents an exception to the rule. The Thundertrap features seven thick (0.25 inch, 6.4 mm) machined baffles of slanted sidewall type. The slanted sidewall concept was developed at Qual-A-Tec and patented by Charles A. “Mickey” Finn. The slanted sidewall is covered by Finn’s U.S. patent number 4,588,043 as well as by patents in Europe, Australia, and South Africa. Lynn McWilliams licensed this technology when Qual-A-Tec closed its doors in 1990.

The slanted sidewall is a diagonal slot of similar radius to the bullet passage, centered on the bullet passage, that creates a diagonal channel going from one side of the rear surface to the opposing side on the front of the baffle. Each slanted sidewall baffle creates a gas jet to push against the stream of combustion gases following the bullet. The gas jet dumps significantly more energy inside the suppressor than the same number of similarly spaced conventional baffles.

Each Thundertrap baffle incorporates an integral, smooth conical spacer that features a mouse-hole adjacent to the forward edge of the slanted sidewall, which directs its gas jet into the coaxial expansion chamber formed by the spacer. This increases the effectiveness of that chamber. The front end cap, which is welded in place and features a recessed face to reduce weight, features a machined inside surface designed to maximize turbulence in the forward-most suppressor chamber. The primary expansion chamber is the smallest I’ve ever seen. While the first baffle reflects some gas into a small space surrounding the threaded portion of the rear end cap, which is welded in place, this chamber by itself does very little to lower the pressure of expanding combustion gases. The sophisticated nature of this overall design not only works the expanding combustion gases very hard, it also generates a substantial frequency shift in the sound signature. The altered frequency of the suppressed muzzle blast significantly enhances a human’s subjective evaluation of the sound signature. Suppressor cognoscenti are always impressed by the “sweet sound” produced by the Thundertrap.

Contrary to my early biases against two-point mounts for centerfire rifles, using a single-point mount for the Thundertrap was a wise decision. Admittedly, a two-point mount that actually stretches the barrel when tightened against a shoulder in the barrel (like the arrangement used in the Qual-A-Tec M89 suppressor) probably confers an accuracy advantage at 1,000 yards, but few of us work at this range. The single-point mount of the Thundertrap will probably deliver superior accuracy on most factory sniper rifles and some custom rifles over suppressors featuring a two-point mount and a bullet passage of similar diameter to the Thundertrap.

This is because rifles like the Remington PSS and comparable factory rifles without very expensive custom barrels typically have bores with surprisingly and significantly variable concentricity. This increases the likelihood of baffle kiss or baffle strike with a two-point mount unless the barrel is removed and turned between centers, at least as far back as the suppressor will extend. The bores of some factory sniper rifles are so out of true that even this labor-intensive mounting process may not be enough to avoid degraded accuracy.

Remember that a bullet wobbles about its axis when it leaves the bore, since its geometric center is never precisely the same as its center of gravity. A bullet won’t “go to sleep” until well down range. Therefore, suppressor alignment is a critical issue, especially with long bullets and suppressors that have relatively tight bullet passages.

It is important to realize that even many custom rifles can require this extra care of turning between centers, unless barrels of exceptional concentricity are used. Using a single-point mount eliminates the need to turn the last 6-9 inches (15-23 cm) of the barrel to ensure concentricity. Only the threaded portion of the barrel need be concentric. Of course, the shoulder behind the threads still needs to be absolutely perpendicular to the bore. Thus, the portion of the barrel to be threaded should still be trued between centers on a lathe.

Another important point when considering subsonic ammunition is that a boat tail bullet exiting the barrel at subsonic velocity wobbles more than a flat-based bullet. This makes suppressor alignment particularly critical if subsonic ammunition with boat tail bullets will be employed. Furthermore, only flat-based bullets should be used in subsonic rounds employed with suppressors that have a relatively tight bullet passage like the Thundertrap. Boat tail bullets driven at conventional supersonic speeds will work splendidly in the Thundertrap, however.

Whether one is using a single-point or a double-point mount, it is worth noting that a relatively short stiff barrel will generally provide superior accuracy with a suppressor compared to a long barrel. Avoid lightweight sporting barrels when suppressing a centerfire rifle. A stiff barrel common to sniping and varmint rifles of 18-20 inches (46-51 cm) can be expected to provide much better accuracy with a suppressor than the very same barrel left at 24-28 inches (61-71 cm). I prefer a 20 inch barrel for the very slight increase in velocity over a barrel of 18 inches, although the velocity difference is not really important for realistic law-enforcement applications.

The Thundertrap replaced the Spectrum 90 in AWC’s product line. Available for rifles chambered from .22 centerfire to .300 Winchester Magnum, the Spectrum 90 was also fabricated entirely from 304 stainless steels. It was 8.3 inches (20.9 cm) long and 1.6 inches (4.1 cm) in diameter. The Spectrum 90 weighed 26 ounces (720 grams) and was finished in a matte black chrome sulfide. It also featured a single-point mount.

I tested the performance of the Thundertrap using the specific equipment and testing protocol advocated at the end of Chapter 5 in the book Silencer History and Performance, Volume 1 (Paladin Press, P.O. Box 1307, Boulder, CO 80306; 800-392-2400). Testing conformed fully with MIL-STD-1474C. Sound pressure levels (SPLs) were measured 1 meter to the left of the muzzle and represent a mean (average) value of 10 shots. Velocities were measured using a P.A.C.T. MKIII timer/chronograph with MKV skyscreens set 24.0 inches apart and the start screen 8.0 feet from the muzzle (P.A.C.T., P.O. Box 531525, Grand Prairie, TX 75053; phone: 214-641-0049). Velocity data also represent the mean value of ten shots. The Thundertrap was tested with supersonic and subsonic ammunition at 93°F (34°C)

Since few people have an intuitive grasp of decibels, a few comments will help put these sound test data into perspective. Decibels are a logarithmic rather than a linear scale that approximates the response of the human ear much more closely than raw sound pressure levels as measured in Pascals. The threshold of human hearing is 0 decibels, a quiet conversation is about 56 dB, an IBM Selectric II typewriter is 84 dB, a Daisy Red Ryder BB Gun is 101 dB, an integrally suppressed Marlin 780 rifle from Jonathan Arthur Ciener is about 124 dB, a .22 CB is about 131 dB and a standard velocity long rifle is about 137 dB when shot from a bolt-action rifle, hearing damage begins at about 140 decibels, the pain threshold is about 141 decibels, an MP5 is about 157 dB, a .45 pistol is about 162 dB, an M16 is about 165 dB, a 122mm howitzer is about 183 dB, and death of the observer can occur in the neighborhood of 220 dB. Most adults can distinguish a 1 decibel difference between impulse sounds such as suppressed gunshots.

Purists will note that a conversation is continuous (RMS) sound, while the other values are impulse sound. And the body does respond differently to these two types of sound. For example, the pain threshold is commonly 140 dB for RMS sound and 141 dB for impulse sound. But including an RMS value in this series of benchmarks is still appropriate, since there are few impulse sounds in our common experience quieter than a BB gun.

It is important to note that the unsuppressed “sound signatures” (more properly called “sound pressure levels” or SPLs) may differ from test to test. This is because different atmospheric conditions (such as temperature, humidity and altitude) affect the burning characteristics of gunpowder. Even the speed of sound changes with the temperature. Therefore, the unsuppressed weapon signatures are always remeasured each day of testing, as a control or benchmark.

The best way to compare suppressors tested under different conditions is to subtract the suppressed sound signature from the unsuppressed sound signature, to get the AMOUNT of suppression. This more useful number is called the net sound reduction.

Using Federal 168 grain (10.9 gram) .308M JHP 7.62x51mm ammunition through a Remington Model 700 Varmint rifle with 20 inch (51 cm) barrel and 1 turn in 12 inch (30.5cm) rate of twist, the unsuppressed sound signature was 165 decibels and the muzzle velocity was 2,611 fps (796 mps). With the Thundertrap suppressor mounted on the rifle, the SPL dropped to 142 dB, for a net sound reduction of 23 dB. First-round pop was just 2 dB, and the .308M produced a muzzle velocity of 2,690 fps (820 mps). Thus projectile velocity was significantly greater with the suppressor installed, thanks to the pressurized and very small primary expansion chamber, and the relatively tight bullet passage inside the suppressor. This phenomenon is called freebore boost.

The Thundertrap was significantly quieter in an earlier test at 68°F (20°C) which employed the very low-flash Remington 150 grain (9.8 gram) JSP round. Using Remington fodder (which is good but nowhere near as accurate as the Federal .308M match ammunition in my experience), the unsuppressed SPL using a Remington PSS rifle was also 165 dB, but the unsuppressed sound signature was an impressive 138 dB, representing a net sound reduction of 27 dB. In both cases, the Thundertrap generated a substantial frequency shift, so the suppressed sound signature seemed a lot quieter than the numbers suggest. This can has a very pleasing sound for a .30 caliber suppressor using supersonic ammunition.

Using 7.62x51mm 180 grain (11.7 gram) SPT subsonic ammunition from Black Hills Shooters Supply (P.O. Box 4220, Rapid City, SD 57709; 800-289-2506), the Remington Model 700 Varmint rifle produced an unsuppressed sound signature of 157 decibels. When the Thundertrap suppressor was fitted to the rifle, the sound signature dropped to 127 dB, which is the same SPL produced by a factory original MP5 SD chambered for the 9x19mm cartridge. Using Black Hills 7.62x51mm ammo, the Thundertrap delivers an impressive 30 dB net sound reduction. First-round pop with the Black Hills ammo was 3 dB. Muzzle velocity was 1,086 fps (331 mps), and the speed of sound at the time of testing was 1,152 fps (351 mps). The Thundertrap did not generate freebore boost with subsonic ammunition. Figures 1 and 2 compare the external ballistics of the Federal .308M supersonic and Black Hills subsonic ammunition.

This was a very stealthy system with subsonic ammo. Accuracy was somewhat disappointing, however, since the Remington has a relatively slow rate of twist for long subsonic projectiles. A 1 in 8 to 1 in 10 twist rate would probably have provided better accuracy with the Black Hills subsonic ammunition. The Savage Tactical Rifle with its 1 in 10 rate of twist, for example, significantly outperforms the Remington PSS with subsonic ammunition in my experience. The one constant regardless of ammunition or rifle type is that the Thundertrap provides excellent performance with precision tactical and sporting arms of all persuasions.

It would not be an overstatement to say that the Thundertrap suppressor from AWC Systems Technology is an important achievement in the history of suppressor design. It is remarkably quiet to the ear, it actually enhances the accuracy of a good rifle by reducing barrel harmonics, and it seems to cut felt recoil nearly in half. Accuracy can be optimized by shortening factory sniper or varmint rifle barrels to approximately 20 inches, or by using a relatively short, stiff custom barrel. Finally, the Thundertrap features robust construction that is suitable for the most demanding applications of the armed professional or the serious sportsman. The Thundertrap is a classic, and I can recommend it without reservation.

AWC Systems Technology
P.O. Box 41938
Phoenix, AZ 85080-1938
phone 602-780-1050
fax 602-780-2967