By Mark White
The Use of Sound Suppressors on High-Powered Rifles
This article will deal with choosing, loading and using accurate subsonic rifles. Unlike the more powerful supersonic rifles, whose bullets generate their own supersonic crack, subsonic rifles are capable of delivering very quiet, almost undetectable, accurate fire. The sound of a subsonic bullet whizzing through the air at 1,000 fps is very quiet indeed, certainly less than an arrow from a bow at 200 fps. We won’t get heavily into the science of it, but a velocity of 1,000 fps (or roughly 300 meters per second) has long been considered optimal, since well before World War II. Any slower, and we’re leaving precious velocity on the table. Any faster, and one runs the risk of breaking into the sound barrier (1,100 fps) in a hot environment, where gunpowder burns more effectively. A warm barrel or a hot cartridge can easily push velocity up another 150 fps, even though the cartridge contains a bullet of the same weight and powder charge.
With a properly designed system, the loudest sound will be that of the bullet strike. With effective suppressor technology we can all but eliminate the sound of a muzzle blast. By hovering around 1,000 fps we can virtually eliminate bullet flight noise. The only thing left is the plop of bullet impact, which can be quite loud on occasion.
Subsonic bullets travel much slower than high-powered rifle bullets. Since the formula for energy squares velocity, it can be seen that the subsonic bullet must try to make up for the loss of power with mass, clever bullet design and accurate shot placement.
One standard formula divides velocity squared by a factor of 450,400. That, times the bullet weight in grains, will equal energy in foot pounds. Let’s take a 200 grain, .308 bullet and crunch some numbers. At 2,400 fps that bullet will deliver 2,558 foot pounds of energy. At 1,000 fps the same slug will only deliver 444 foot pounds of energy.
A 300 grain, .44 Magnum bullet driven at 1,000 fps will delivery 666 foot pounds of energy. A 55 grain, .223 bullet will develop 1,250 foot pounds of energy at 3,200 fps. While the energy of a .223 on paper may be twice that of the .44 Magnum, the 44’s greater mass and deeper penetration will prove far more deadly on large animals. In the 1960s the friends and family of the Ruger empire spent quite a bit of time in Africa with their .44 Magnum, semi-auto carbines. Most who used those .44 carbines were very impressed with their lethality. The .44 is a lot more effective than the paper ballistics would lead one to believe.
For those who enjoy playing with calculators, a factor of 2.22, times the proposed bullet weight in grains, will equal foot pounds of energy at a velocity of 1,000 fps.
Barrel Length and Porting
One doesn’t need much barrel length to develop a minimal 1,000 fps of velocity with a heavy, large caliber bullet. An 8 to 10 inch tube will provide plenty of acceleration. For the record, a good 10 inch barrel is fully as accurate as a much longer one. One more time, with feeling, a 10 inch barrel is fully as accurate as a 30 inch barrel. We often note a significant increase in accuracy when we cut a 24 inch barrel back to 10 inches. A proper chamber, adequate rifling twist rate and a perfect muzzle crown are all more important than barrel length.
If porting (holes drilled in the barrel to bleed propellant gas) is used as one of the devices to reduce the noise of a suppressed firearm, it is recommended that the barrel be from 10 to 12 inches in length. Porting, when properly executed, can reduce a suppressor’s overall report by as much as 40%. All ports should carry a substantial 45 degree bevel at the bore interface, or they will shave off copper or lead from the bullets, which will pack up the primary expansion chamber and the ports themselves. If a suppressor eventually weighs 8 pounds more than it used to, there is a good chance that sharp or burred ports are at fault. Many manufacturers bevel the outside of each port, but this does little or nothing to cure the problem. Beveling the inside of each port is not easy, but it must be done.
For private ownership in the U.S., a pistol barrel may be of any length. A rifle barrel must be over 16 inches long. Any shorter, and a $200 Federal tax stamp (and a Form 4) will be due on private ownership. Municipality, county or state ownership of a short barreled rifle or suppressor will of course require federal registration, but no tax stamp will be due.
Caliber Selection and Bullet Shape
Since velocity is rigidly fixed, the most important area of the selection process will be based on the assigned role of the firearm. Plinkers and target shooters are well served with the common .22 LR round. It’s cheap, quiet, available and accurate. The high-speed .22 LR round is transonic, which means that it starts out faster than 1,100 fps (supersonic) but then its velocity decays into the area where parts of the bullet are supersonic, and parts are not. When a bullet travels through the transonic range the frictional pull trying to slow it down is from four to five times greater than the pull that exists at subsonic velocity. Simply put, this differential pull causes instability. A stable, round-nosed, flat-based bullet (like the .22 LR) will be less accurate in the transonic range. Inherently unstable, hollow-point, boat-tailed bullets (with the preponderance of mass to the rear) will lose all stability in the transonic range, tumbling end-over-end and losing any semblance of accuracy at that speed. Thirty years ago, those who drove Chrysler vehicles on slippery roads in the northern states found that, in a situation where control was lost, the vehicle would spin and settle into a rear end-first attitude, because the rear end was heavier than the front end. Those who drove Ford products (which typically had less rear-wheel traction on ice) soon learned that the heavier front end caused the vehicle to be more stable in a spin. Its natural movement in a minimal traction situation was front-end first. Sharply pointed bullets have the heaviest end at the rear, and they take a much greater spin rate to keep them pointed in the right direction. Bullets with blunt points and hollow bases (Like hollow-based, wadcutters) are inherently stable in flight. They fly straight, even without spin.
In terms of effectiveness on live targets, it is very hard to beat a blunt-nosed or flat-tipped bullet. Put another way, a subsonic bullet that is a true cylinder will deliver more shock, hemorrhage and trauma than any other shape. Sharply pointed and round-nosed projectiles will slip right through, while causing minimal damage. It has been said that some .30 caliber projectiles are designed to expand at 1,000 fps, but this remains to be proven to my satisfaction. Sharply pointed bullets will penetrate deeply at subsonic velocities – pushing nerve tissue and blood vessels aside, rather than cutting them. Unless the bullet hits the base of the brain or a major nerve center, the animal will run away, usually to die a slow and agonizing death. Most pointed and round-nosed .30 caliber rifle bullets are totally lacking in knockdown power at subsonic velocities. We hear the same stories of subsonic .30 caliber bullet inadequacies over and over again, and are frankly quite tired of them. Subsonic .30 caliber bullets will not expand in large animals. The only effective .30 caliber subsonic bullet will have a totally flat front end.
For those entities involved with animal control, the subsonic .22 LR round is relatively humane (meaning it kills quickly) and effective on animals weighing up to roughly 20 pounds. On snakes and small vermin the Remington Subsonic, hollow-point round is fairly effective. It usually stays subsonic, even in long, unported barrels, and is fairly accurate. On very small rodents a round called the .22 CB Long offers reduced bullet weight and less penetration. It is not a very accurate round, but works OK for squirrels in attics and pigeons inside barns at close range. It will sometimes penetrate a sheet metal roof, so one must be careful regarding a backstop. On larger, tougher animals CCI’s SGB (small game bullet) offers extreme accuracy and deep, effective penetration. Unlike high-velocity hollowpoints, which often fragment and perform poorly, the SGB is one of the first modern attempts at scientific design in a rimfire cartridge. Its bullet is of hardened lead, with a solid, but slightly flattened tip. If I were going to pack a small .22 rifle into a wilderness survival kit, it would be accompanied by a large supply of SGBs. They work well on small animals, and work better than any other .22 LR round on larger animals. Until someone comes up with a .22 LR wadcutter (I hope CCI is listening) the SGB will remain the most effective .22 rimfire round available.
The next stop up the ladder of higher subsonic energy is the move to a .30 caliber weapon. The .308 is a logical place to start, and (with a light charge of fast powder) it can be effective in a weapon that is designed to be both subsonic and supersonic. A 1 in 10 inch twist will stabilize up to a 200 grain, round-nosed, flat-based bullet. However, the extra room in the .308 case provides a substantial cushion, which can cause problems with efficiency and consistency. The most ideal situation results when a cartridge case is just big enough to hold its charge of powder and a bullet, with no room to spare. In the 60s a fellow named Joe Apache necked a .223 case up to .30 caliber. The result was an interesting cartridge called the .30 Apache, which sat ignored for quite a number of years.
Eventually the use of suppressors burgeoned in the U.S. and Grendel Arms (now known as Keltec) began experimenting with a similar case in a suppressed M16. The concept eventually developed into what is now known as the .300 Whisper. That small .30 caliber cartridge will easily launch a bullet as heavy as 250 grains at a subsonic velocity. Not surprisingly, the longer, heavier bullets have to be spun at a full turn in 6 to 8 inches in order to stabilize at low velocity. Again, it has been said that some of these heavy bullets will expand at subsonic velocity, but I’ve seen absolutely no evidence of it. Indeed, they usually perform like a knitting needle, poking a small, straight hole, in one side and out the other, wasting 90 percent of their limited energy beyond the primary target. I’ve heard the word tumble used in conjunction with the .300 Whisper, but I’ve not seen that happen either. The heavy bullets are capable of extreme penetration, but I have seen absolutely no inclination towards tumbling. Many have had great expectations for the subsonic Whisper cartridge, but until they develop a flat point for a hard, .30 caliber bullet, I feel that they will continue to be disappointed.
Dr. Martin Fackler, founder of International Wound Ballistics Association, devoted a considerable amount of research, study and experimentation to the subject of subsonic bullets. Based on his own and other research going back 200 years, Dr. Fackler (in a nutshell) concluded that hollowpoints and expanding bullets are a waste of effort. One can do no better than to use a simple, hard-cast lead bullet with a totally flat nose, and with sharp edges at the transition between the flat face and the cylinder walls. Such a bullet does not move through the air with the extreme ease of a VLD (very low drag) bullet, but its terminal effect is considerable.
The next logical step up in caliber is to .338. In the early 70s, Max Atchisson of Georgia cut off the shoulder of a .223 case and trimmed it to an overall length of 1.412 inches. The result was a case mouth of the perfect size for a .338 bullet. Called the .338-223 Straight, the cartridge is of great interest. Like the .300 Whisper, it will launch a heavy bullet very quietly. I am told that either of these efficient bullets will arrive at a target 300 yards distant with a loss of less than 100 fps. Those who are used to supersonic bullets will find this astounding, but one must remember that it takes a lot of energy to break the sound barrier on a continuous basis. A subsonic bullet that isn’t wobbling in flight is the Honda Civic of the firearms world. It moves through the air with a velocity decay rate roughly one-fourth the rate of a supersonic bullet. Until we get a flat-nosed .338 bullet, this cartridge will also suffer from the same knitting needle-like effect.
We could stop to visit with the .38, but I’m going to bypass that and settle on the .44, which is really .43 (actually .429) caliber. Ruger now makes a lever-action and a bolt-action rifle, both of which are chambered in the powerful .44 Magnum cartridge. We’ve been waiting for twenty years for these rifles, and are immensely pleased that they are finally on the market. Wadcutters and flat-nosed, cast bullets are available in weights from 185 to 300 grains. For those who hand cast, the weights range from 80 to 362 grains. Since factory ammunition is usually too fast, the subsonic .44 Magnum rifle is a handloading proposition. Fortunately, Mike Dillon’s Square Deal press is affordable, and cranks satisfactory rounds out at a prodigious rate. The twist in Ruger’s .44 barrel is 1 turn in 20 inches, which seems to stabilize 300 grain bullets effectively. It should be mentioned that, while barrel leading can be a problem with lead bullets driven beyond 1,400 fps, it will not be a problem with lubricated, hard-cast bullets driven to 1,000 fps. We should also mention that we’ve been buying plain-based, hard-cast, lubricated lead bullets from Brownells, and that we shoot them backwards in order to get the maximum effect. Midway, Dillon and quite a number of other suppliers sell swaged or cast lead, lubricated bullets for both the .44 and the .45. We don’t care about ballistic coefficient nearly as much as we care about terminal performance, which has been rated as nothing short of excellent by contractors, animal control officers and park rangers. The flat-nosed .44 delivers a mighty whack. It has excellent knockdown power. It isn’t a good 300 yard weapon, but remember, we’re talking subsonic here. Any bullet that moves at a sedate 1,000 fps will have a rainbow-like trajectory much beyond 100 yards. Little velocity is lost, and the weapon is still very accurate at extreme range, but finding the proper elevation adjustment can be tricky.
The powders of choice have been the time-honored Unique and a powder made in Finland by Vihta Vuori Oy called N 310. The Germans developed a very fast powder for their suppressed rifles during World War II, and this may be a very close duplicate of that powder. It should be mentioned that the Finns turned some of their subsonic rifle bullets backwards for better accuracy and improved terminal performance. They also developed a system using a few drops of solvent to dissolve the upper layer of their fast powder. After this solvent evaporated, the powder was thus sealed into the rear of large-volume cartridge cases. A bullet was then seated and heavily crimped in place. This helped to achieve better combustion and improved uniformity. Prior to this a filler, such as nitrated cotton fiber or kapok, had been used on large-volume shells. The solvent was a stroke of genius because it rapidly evaporated, did the job very effectively, and left nothing extra inside their suppressors.
Interestingly, we were using N 310 powder in a Thompson Contender, which developed the disconcerting habit of opening up by itself each time it was fired. Curiously, no damage occurred, and the bullets hit the target as though nothing was amiss. The standard pistol primers did not indicate any sign of high pressure. The velocity was 1,000 fps, out of a 21 inch, unported barrel. After this happened several times in a row we switched to Unique (a slower powder) and the problem went away.
H & R and NEF also make a single-shot, break-open carbine, chambered in either .44 Magnum or .45-70. These rifles are more robust than the Thompson Contender, and remain closed when fired, regardless of the load. At a mere $150, these are the cheapest games in town. Don’t think that inexpensive means unreliable or inaccurate. These are very reliable, accurate weapons. More so than the expensive and finicky Contender.
Dating back to 1873, the .45 Colt is a close cousin to the .44. This rimmed cartridge offers 10% greater frontal area. The caliber and the cartridge were the end product of a lot of cut-and-try research. The .45 Colt may be old, but it certainly isn’t obsolete. Many who hunt deer with a revolver feel that the .45 Colt is as close to perfection as one can get. We really like the cartridge, but are having a hard time finding rifles we like with the .45 Colt chambering. Winchester and Marlin both make lever-action rifles, but the feed tube is tied to the barrel and gets in the way of the suppressor. We’ve been buying .45 Colt barrels with a 1 in 14 inch twist from Bullberry in Utah for the single shot, Thompson Contender. We look forward to the day when H & R, RUGER and NEF make their rifles in .45 Colt.
The .45-70 cartridge seems like an obvious step beyond the .45 Colt. We’ve suppressed this round but are not as happy with it as we are with the .45 Colt. The Colt has a slug with a .451 inch diameter and is available with bullet weights up to 425 grains. As a cartridge, the Colt is compact and easily loaded. Its case walls are heavy and durable. The current popularity of cowboy action shooting make the .45 Colt cartridges readily available, and inexpensive. The .45-70 has a bit more capacity than we really like, and its case walls are quite thin near the mouth. The mouth is easily bent or deformed. We’ve crumpled and ruined quite a number of .45-70 cases while attempting to resize or seat bullets. The diameter of the .45-70 is .458 inches. Cast bullets are available in weights up to 645 grains, which ought to be plenty for almost any situation we can envision in North America.
Some have attempted to suppress the mighty .458 Winchester Magnum. That is truly a waste of effort, as there is absolutely no difference between the subsonic .458 and the subsonic .45-70, other than that the .45-70 is more efficient because its case capacity is smaller. We’re not saying no to either the .45-70 or the .458, it’s just that we like the .45 Colt a lot more. The .44 Magnum and the .45 Colt suppressed rifles are perfectly suited to the task of quietly harvesting or removing animals weighing between 100 and 600 pounds. Both cartridges are supremely accurate and very efficient at subsonic velocities. The ideal weight of bullet will drive completely through the animal in questions, remaining just under the skin on the far side. This is a close to perfection as it gets. The .44 Magnum and the .45 Colt have excellent knockdown power when loaded with bullets having absolutely flat front ends.
The only possible improvement over the .44 and the .45 Colt would be a move to the legal maximum diameter in the U.S., which would be .50 caliber. Interestingly, the French were among the first to do this in the 1870s, when they fitted one of the first metallic silencers to a .50 caliber Remington Rolling Block pistol. The.50 Remington (M71 Army) used blackpowder to drive a 300 grain lead bullet along at a sedate 600 fps. The powder was corrosive, and the suppressor would have to be boiled out with soap and water, and then oiled after use, or it would eventually be destroyed by corrosion. Rimmed .50 caliber cartridges can be made from 50-70 brass, an expensive and laborious tasks. A wadcutter bullet would have to be designed in .50 as this is not an item which is readily available. The .50 caliber offers almost 20% greater frontal area over the .45. A bullet weighing between 400 and 1,000 grains would seem appropriate for this caliber. Again, we have been very happy with the .44 and the .45 Colt, and find a need for anything beyond these two cartridges unlikely.
Brownells, Inc., 200 S. Front St., Montezuma, Iowa 50171. Phone: 515-623-5401, Fax 515-623-3896
Bullberry, 2430 W. 230 N. 67-5 Hurrican, Utah 84737. Phone: 801-635-9866
Dillon Precision Products, 8009 E. Dillon’s Way, Scottsdale, AZ 85260-9865 Phone: 800-223-4570, Fax 602-998-2786
Midway, Box 718, Columbia, MO 65205. Phone: 800-243-3220, Fax 573-446-1018
NEI Handtools, a supplier of custom bullet molds, 51583 Columbia River Highway, Scappoose, OR 97056. Phone: 503-543-6776, Fax 7865
|This article first appeared in Small Arms Review V1N9 (June 1998)|