By Thomas T. Hoel, historical and technical editing by Dan Shea, Photos by Dan Shea

There always seems to be a certain few military firearms that bear an unusual and universal interest for collectors and students of military weaponry. The US M60 General Purpose Machinegun has always occupied just such a position within the civilian NFA weapons owning population. Although there also seems to be little ability to compromise on feelings toward the design, as it is either highly praised or deeply maligned. While in the past literally volumes have been written on the military adoption and use of this interesting weapon, the scope of this discussion is strictly to aid the civilian owner-operator of the M60 GPMG as a guide in obtaining maximum enjoyment, usefulness, and longevity of his personally owned machinegun.
Additionally, specific recommendations discussed herein for operations strictly in the civilian realm will be presented as the civilian owner-operator has certain freedoms, and also certain limitations, that the original military end-users may not. The M60 has a number of well-known characteristic wear and failure profiles for certain component parts and assemblies. Anything the civilian owner-operator can do to decrease operating stresses, and attendant wear and tear on component parts or assemblies, will serve to prevent unnecessary or premature wear and failure of these parts, adding tremendously to the life expectancy, serviceability, and enjoyment of the weapon as a whole. This should be the primary concern with such the large investment these privately owned machineguns represent.

While certain distinct characteristics of the M60 design may not at all pose a serious or dangerous matter for the civilian owner in a recreational shooting environment if or when they result in a failure to function, they bear discussion to further the serviceability and enjoyment of personally owned examples. This discussion is divided into two distinct sections. The first, discusses in detail the receiver, its sub-components and construction, along with recommended practices for the care and preservation of the receiver as an assembly. The second part will discuss the various and sundry peripheral assemblies that complete the weapon, with the same emphasis in the discussion provided as appropriate.

Many of the long established military use and service protocols exist for reasons specific to the military/combat environment, or specific governmental exigencies. These include repair or service protocols where the actual military end-user is not to be concerned with the costs of repair, even if the supply of spare parts was unlimited. Since the civilian owner-operator is not bound by such exigencies, he should exploit any and all maintenance and operating schemes that benefit preserving of the serviceability of the weapon over an extended period of time and use, along with minimizing actual financial outlays for avoidable repairs parts or services. As such, certain of these recommendations are intended for use only in the civilian realm, and do not represent advice or recommendations for operational use, or maintenance functionality, of the weapon in any military or law enforcement scenarios.

The Heart of the Matter

Those M60 machineguns that are available to the civilian collector of NFA weapons can be described as being of two basic origins. The first important distinction, and the one which relates most strongly to their value as collectibles only, concerns the manufacturing origins.

The top rung on the collectability ladder is those guns that were originally manufactured by a genuine military contract producer. Although their numbers are quite small there are, remarkably, a certain number of M60’s that are of true military production-line origin and pedigree. Due to these contract producers being private companies, they were able to offer the exact same weapons they were producing under military contracts additionally to both domestic law enforcement entities, or for export to approved Friendly Nations clients. Not all guns originally destined for either of those last two markets ended up there, mainly due to some quirks in salesmanship domestically, and thus a few of those guns have been able to enter the civilian market and placed into the NFRTR. The salient feature of these specific guns is that they can all be described as being manufactured and assembled to full military specification, in both materials and workmanship, in all component parts and assemblies. While this distinction often has no bearing on serviceability for sport shooting purposes, it can have a definite in their value. The second group of guns is that in which the receiver was manufactured by any method, by anyone, other than the original military contract producers. This is the most critical distinction in the pedigree (and value) of civilian available M60 guns, and bears careful discussion.

Receiver Basics

The “receiver” of the M60 machinegun on all of its several variant models is actually an assembly of several component parts, permanently or semi-permanently joined to render the complete functional assembly. BATF Technology Branch has recently authored a reply to an inquiry letter asking for a definition of what legally constitutes an M60 machinegun “receiver.” By rendering this recent official opinion they introduced considerable confusion into what was previously the legal definition under previous Technology Branch Administrations. The “current” (as of 11/2001) BATF Technology Branch definition of a “M60 machinegun receiver” is: “…the frame or receiver of the M60 machinegun consists of a bottom plate(sic), two side plates(sic), the bridge, and a trunnion. The top cover, while attaching to the receiver, is not considered a part of the receiver.”

This definition is significant as it fails to consider two of the most structurally important receiver component pieces, namely the receiver’s sheet metal channel and the gas tube. Both parts are structural members that are permanently joined to form the receiver structure, and in the case of the sheet metal channel, to which the above mentioned five component parts must be joined together.

The “receiver” of the M60 machinegun has traditionally been defined to be made up from eight permanently assembled individual component parts, as follows:

• Barrel trunnion
• Gas tube (or Operating Rod tube)
• Stamped sheet-metal “lower receiver channel”
• Left and right side, milled, bolt bearing/guide rails
• Lower, milled, operating rod guide channel (similar to the bolt guide rails)
• Stamped rear receiver “ridge” (top cover latch)
• Mounting plate, T&E mechanism adapter.

(There may be one possible additional component part not counted above. Some very early military trunnions utilized a separate, riveted-in, cartridge feed ramp. This was soon replaced in the manufacturing process by a simple machined ramp feature in the basic trunnion forging. Virtually all, new-manufacture, commercially produced trunnions have the machined in feed ramp feature.)

These above eight component parts are assembled, by either riveted and/or welded joints, into a unitized structure that cannot be disassembled to a lower individual state without destructive separation. This is a significant definition, as it relates to what BATF Technology Branch is using now to determine the legal definition of a “M60 machinegun receiver.” By electing to render this current definition, BATF Technology Branch has ostensibly recognized the true component nature of the M60 machinegun receiver, thereby presumably allowing a duly registered weapon to have any of its five legally defined component receiver parts replaced if necessary due to damage. (While it is of course prudent to get a personal reply to any proposed repair actions inquiry direct from Technology Branch, this “opinion” has been rendered verbally to others in the past) The relevant statement from the recent opinion states: “…removal of one or more of these (component) parts would not change the classification of the item as a machinegun.”

This statement, making no mention of the other two common, and structurally required, component parts, can be assumed to indicate that they do not comprise a part of a “machinegun receiver” in the current opinion of ATF and are of no consequence in its definition. However, this now introduces considerable confusion into individual guns being compliant with the markings requirements (Title 26 U.S.C., Chapter 53, section 5861(g)), as there now exists a discrepancy between their (recent) definition of the “receiver” and where certain older, Pre-5/19/1986, registered machineguns bear their legally required serial number(s), which by the recent definition, can be located on a part that is not now considered to be the “machinegun receiver, or a component part of a machinegun receiver.”

This utterly bizarre and unexplainable situation becomes highly relevant when one observes that the legally required manufacturers’ identification markings and required serial number(s) have been observed to have been applied to at least three of the major “receiver” components when examining individual commercially manufactured guns, which by the recent definition can be located on a part that is not now considered to be the “machinegun receiver, or a component part of a machinegun receiver.” The most common location to place these required markings have been the top surface of the barrel trunnion, the large flat surfaces of the sheet metal channel, or the bottom surface of the gas tube, with only the trunnion now being legally considered a component part of a machinegun receiver. (It should be noted that all of those guns that were originally manufactured by a genuine military contract producer bear their markings on the top surface of the barrel trunnion.)

In addition to these above described permanently assembled component parts, a functional M60 receiver is usually considered to also comprise the following semi-permanently installed components or assemblies, (Though these additional parts are required for a functional weapon, they do not comprise the legally defined receiver.):

• Rear sight assembly (any variant model specific assembly)
• Carrying handle assembly (M60 and M60D only)
• Tripod pintle retaining latch pin
• Cocking handle assembly (cocking handle and cover plate)
• Barrel retaining latch mechanism

It is important to understand that in the sense that though the “receiver” of the commercially produced M60 machinegun may bear markings of a Class 2 Manufacturer, only a select few parts are not original military contract origin parts. Usually in most cases, the only component part(s) known to be actually made by these civilian concerns was the barrel trunnion itself, though in some cases additionally the sheet metal channel, and/or the bolt and operating guide rail sections were of new, commercial fabrication. The remaining component parts or assemblies used to complete the weapon were simply military contract spares, commonly available on the surplus market. This was a simple necessity from practical reasons as since the barrel trunnion was the most massive and sturdiest component in the receiver design, its failure or damage in service was not seen as a common occurance, hence a supply of ex-military origin spare-part trunnions was virtually non-existent. Unlike most other common spares or replacement parts of the gun, barrel trunnions as spares simply never really reached the surplus markets, so they had to be fabricated on the civilian side. The other reason is that even in the military environment, the barrel trunnion was considered to be the (tightly) controlled part of the weapon (“the receiver”) as it bore the manufacturers markings and serial number. The remainder of the receiver components could generally be obtained, so that from that point on the “manufacture of a civilian M60 was nothing more than proper assembly of the component parts and assemblies needed to render whatever version of the gun you were trying to build. In general terms then, the civilian M60 machinegun is built up from all MIL-SPEC parts and assemblies, with the exception of certain receiver parts. How this was accomplished was not always the same, either from a mechanical standpoint, aesthetic, or “quality” perspective.

Trunnion Variations

Excluding the few guns that came from the true military contract producers, the manufacture of the barrel trunnion is where the greatest difference in civilian M60’s comes into play. The original MIL-SPEC calls for the trunnion to be manufactured from an ordnance steel hammered-pressure forging, machined to final dimensions and tolerances. This is ideal if the economics of a Governmental contract with a large manufacturing concern allow for it, but for the civilian market, such expenses for what was always a extremely limited production item, were simply impossible. Fortunately though, the design of the M60 places no direct firing stresses on the trunnion itself, as the rotating bolt locking into the barrel extension contains these; and these two component parts are MIL-SPEC items in every commercial M60 known.

Due to this fortunate circumstance alternate methods of manufacture for the trunnion were conceivable, and fully within the limits of complete safety. As the M60 barrel trunnion only receives indirect stresses of firing, and since all other highly stressed component parts are MIL-SPEC items, the civilian trunnions could be manufactured by more cost efficient methods. And no matter how the basic trunnion blank was fabricated, all M60 trunnions required machining to final dimensions and tolerances.

All forms of manufacture for the trunnion blanks, be they forgings, castings, or fully machined, require slightly differing methods of arriving at the actual blank form shape as each method must be designed to accommodate the intended metallurgical profile employed. In other words, a blank sized and shaped to be formed from a pressure forging will not be directly the same as one intended to be cast, as the different metallurgies require that different physical areas of the trunnion be formed correctly for the method used. This results in slightly differing exterior shapes and sizes of otherwise “identical” parts that have been manufactured by different methods.

The most commonly employed method for the manufacture of civilian M60 trunnions was by investment casting the receiver blank form, though machining from full barstock or billet was also done. It may be argued that, in theoretical terms at least, a firearm receiver made from a machined billet of solid steel may offer certain theoretical advantages in the metallurgy of grain structure and orientation over a cast-steel version. However, in terms of the commercial M60 trunnions machined out of barstock or billet steel, this perceived advantage is of no consequence. The widespread application of CNC machining tools now being used even in the small-production shops today, was not the case when these receivers were machined and registered close to twenty years ago. At that time, without having access to the extremely expensive pressure forging methods employed in military production line manufacture, investment casting of the trunnion blank was the most reliable method of duplicating the compound curvatures and other hard-to-duplicate exterior forms of the originally designed MIL-SPEC forging. As a consequence, fully machined billet trunnions bear a distinctively more “heavy,” or “squared-off” appearance totally negating the size-to-weight ratio advantages of the strong, but lightweight, forging of the mil-spec original, or even the casting.

Commercial investment-cast steel trunnion guns are every bit as serviceable as their military cousins, and are equivalent in life-limit and durability if the private owner takes certain common sense precautions. Importantly, these castings also virtually duplicate the exact exterior physical contours of the forged original design, and can actually be very hard to tell apart from a MIL-SPEC forging if the telltale surface features of a casting are not known. These cast trunnions are particularly close to the forged MIL-SPEC originals as the basic casting alloy used was an excellent firearms-grade of steel, and the casting process employed produced a nearly exact unfinished blank that required nearly the same machining steps as the MIL-SPEC forging to complete. When finished, these cast trunnions displayed the greatest degree of uniformity of all commercially produced M60 trunnions. They readily accepted standard military component parts and assemblies used to complete the receiver assembly, and mil-spec parts interchangeability is virtually certain.

With those commercial M60 trunnions machined out of barstock or billet steel though, certain Class 2 manufacturers were content with only replicating the functionality of the original military spec forged trunnion. Due to the difficulties in replicating the hard-to-machine contours and compound curvatures of the original forged-blank design, exterior contours were often left in a rougher and not-exact state of duplication on these billet-steel trunnions. Fully machined trunnions are easily identifiable by their more “squared-off” contours, and while detracting from the aesthetics a bit, remain fully serviceable and inherently strong. Fully machined trunnions are readily identifiable due to their telltale machining marks along all major surfaces, and the less pronounced curvatures around the top of the barrel channel and rear sight mounting base. Interchangeability of MIL-SPEC component parts and assemblies on these trunnions can vary considerably depending upon the tolerances of the final machining; many of these fully machined billet trunnions exhibit indications of hand-fitting of individual parts during final assembly. A thorough inspection of an individual receiver for evidence of hand-fitting of parts or assemblies is highly advised, as later fitting of any replacement parts may be considerably more involved than with another type of trunnion based receiver.

In the many decades the gun has been in military service, literally thousands have been removed from service and DEMIL-ed, and then surplused out as scrap value. It is known that over time various methods for the actual DEMIL procedure of ex-military firearms were used, generally becoming more fully destructive over the years as concerns mounted as to usability of even component parts remaining. It is further known that a few M60 ‘s were DEMIL-ed in a more “friendly fashion” leaving open the possibility of salvaging an un-cut trunnion itself, from which a new “receiver” could be fabricated quite easily. It is therefore possible to have a commercial receiver fabricated using an original, un-cut, MIL-SPEC trunnion still bearing military production markings, and while having no collector’s value, it will be desirable receiver. The major problem here is just how the trunnion was originally joined to the other component pieces of the receiver, if only rivets had to be drilled off the DEMIL-ed pieces, it may render a perfect trunnion, but if there was any welding of the other component pieces this can complicate matters. For a DEMIL-ed receiver to have escaped the mandated reinforcing weldments, it had to have been DEMIL-ed very early on, or come from an out-of-the-way locale in the inventory. (While likely exceedingly rare, there a few known to exist in civilian hands, of this exact origin.)

The last variation in available “commercial” trunnions, undeniably the least desirable, are those individual trunnions that have been re-manufactured from original military production guns that have been DEMIL-ed. Commonly known as “re-welded” trunnions or receivers. Usually these re-manufactured commercial production receivers/guns were built up with all new receiver components assembled onto an original military production forged trunnion that has been re-manufactured into a homogeneous component by welding existing-but-damaged pieces back together. Despite any cosmetic touches rendered during final finish to make it appear “new,” original forged trunnions that have undergone welding should be carefully and thoroughly examined. When originally manufactured under military contract production, these forgings were final heat treated to produce casehardened surface hardness of 57-58+ Rockwell C scale. Case hardening is not very thick as it is intended to reduce surface wear primarily, and drops off quickly to a core value in the high 20’s Rockwell C scale. When rejoining such pieces by welding, followed by seam grinding, the basic welding process along these long and deep seams will likely produce micro-granular fracturing and general stress concentrations that can possibly extend to structural cracking and failure in/near the weldments, or along lines of concentrated stress. (This is far different type of welding than the reinforcement welds described above which penetrate only to a very shallow depth, and with minimal linear progression.) To be clear then, a re-manufactured trunnion that has undergone welding is always suspect for cracking and stress failure along the re-joined seam(s). Though generally serviceable as shooters, these re-manufactured receivers warrant close inspection before purchase (a MagnaFlux®, or fluorescent dye-penetrant type, inspection is recommended), and continuously thereafter in service at regular intervals.

In Part II we will begin discussion of the various component parts and their assembly and interface to the basic receiver assembly, along with a continuing look at factors that contribute to the structural integrity of the receiver.

John Moses Browning’s .50 caliber machinegun first roared to life in the closing month of World War One. Astonishingly, it is still in first line U.S. service and with many other armies worldwide today, nearly eighty years later. Although heavy, a bit cantankerous, and really fussy about headspace, the M2 Heavy Barrel Machine Gun is rightly considered by many to be the best in its class. “Ma Deuce” as she has been affectionately known by generations of American military men, is still an indispensable member of the modern small arms family and will remain so well into the new millennium.

Introduction to Part 2

Last month in Part One we explored the developmental history of John M. Browning’s famous .50 caliber M2HB machine gun and its ground, sea and air combat use from WWII through Vietnam. Now, we continue our in-depth study of Browning’s masterpiece, visiting a unit of today’s US Marines as they introduce some of their newest officers to the oldest and longest serving infantry weapon in the American arsenal. Quantico, Virginia is the center of the Universe for the United States Marine Corps and home of its Officer Basic School where newly commissioned Marine lieutenants go for a tough and uncompromising introduction to the most fundamental missions of the Corps. Among the many rich and varied experiences that these young officers will have during their stay at Basic is the opportunity for some hands-on live fire with the family of Marine Corps small arms. Captain George Schreffler, Range 7 OIC for the day, has kindly consented to allowing close in photographs during the day’s training and firing. Wisely, he places me with Sergeant Mayc-o McKeever and his men from Weapons Platoon, CI Company. McKeever, a no-nonsense guy as you might well expect, makes sure I get the opportunity for the full experience by thoughtfully providing a ten pound kevlar flak vest and helmet. This is a real treat and immediately makes me feel just like one of the boys; sweating like a pig on a typically hot and humid southern summer day with the nearest shade some 25 meters behind the firing line. Are we having fun yet?

Role Reversal

One of the day’s unexpected delights for this old retired Army sergeant was the opportunity to see some real Marine NCOs in firm control of some nearly real Marine lieutenants. This seems to be one of those fascinating and little known traditions of the Corps that when young officers are in student mode — which they definitely are at Basic School — the staff is in charge. And there was no doubt that day at the .50 caliber station on Range 7 that Sergeant Mayc-o McKeever, Sergeant Grisson Gamba, and Corporal Tom Senter were clearly in charge. The lieutenants had already spent several days in classroom instruction on tactical theory of crew served weapons and practical mechanical training with stripping, cleaning, assembling and adjusting both the Mark 19 grenade machine gun and the M2 fifty cal. After yet another opportunity that morning to break ‘em down and put ‘em back together, several groups of about twenty made their way in round-robin fashion from live fire stations on these two guns as well as an AT4 subcaliber launcher.

Ammo Point

Their first stop along the way to visiting Grandma Deuce was the ammunition shed, where each Marine was issued a short belt of cartridges — and I mean a SHORT belt. Given the pitiful state of today’s pathetically shrunken military budget and grossly accelerated operational tempo, the Corps can’t afford to give their soon-to-be-real lieutenants more than twenty rounds apiece without dangerously shortchanging forward-deployed Marines! Meanwhile, Clinton seems to think it is fine to give billions to Boris Yeltsin’s Russian kleptocracy and congress seems to consider funding day care centers for unwed military mothers and other politically correct bullshit to be a higher priority. May God help us in any coming wars….(Editor’s note: At this point, the author goes off on a political rant that we decided to spare the readers, who will probably agree with Robert, but we HAD to keep his admonition regarding training ammunition budgets intact- Dan ) Everybody got some pretty spectacular 1991 production Lake City stuff. Each belt featured a regular series of four rounds of M8 API (armor piercing incendiary) plus one M20 APIT (armor piercing incendiary tracer) strung out on M9 metallic links. The M8 is a real crowd pleaser because it produces a very bright flash on impact, giving the gun crew unmistakable evidence of where the rounds are hitting. It also does a particularly nasty bit of work on lightly armored enemy vehicles such as the Soviet BMP and the troops inside.

Listen Up, Sir!

A short walk down the hill brought them to the .50 cal. station, where they gathered in front of Sergeant McKeever who gave them a quick set of do’s and don’t’s. You know the drill: “Welcome to the M2 .50 caliber heavy machine gun station where you will have the opportunity to engage targets at extreme range,” McKeever began with well-practiced professionalism. His five minute refresher course succinctly covered the process of using the rear sight to “dial in” estimated range, then firing short bursts to observe the strike of cartridges in the beaten zone. “Remember your WERM formula exercises (Width Equals Range times Mils),” McKeever sagely offered, helpfully adding that each click of the “T&E” (traversing and elevating mechanism) only moves the gun’s aimpoint one mil (roughly one meter up/down/left/right for each thousand meters of range). Initial manipulation of the T&E, he coached, was best done in increments of five or more clicks with the loader/observer for each two man team specifying how many clicks to the gunner. Noting that the ammunition they had been given consisted of strings of four incendiary rounds followed by a tracer, McKeever took pains to caution them that they should not rely on the apparent path taken by tracers as this gets deceptive at relatively long range. “Watch the dust and flash from your burst,” he cautioned, “that’s where most of the steel is hitting.” Sergeant McKeever concluded his rapid fire refresher with two time-honored and obligatory phrases: “DON’T DO ANYTHING until you are told to. Any questions?” He broke the group down into pairs and put the first set on the ground behind six guns ready on the firing line, then led them step by step through loading drill. The most amusing aspect of this came at the point when feed covers were slammed down to lock and it became necessary to retract the bolt. This is a man’s job, requiring a hefty jerk of the retracting slide handle to not only overcome tension of the gun’s beefy recoil spring, but also to pull the first round out of its snug metal link. Amusingly, more than one lieutenant (probably headed for staff duty) wasn’t able to do this without a struggle. Finally, satisfied that everybody was ready, Sergeant McKeever gave the order to commence firing.

Despite McKeever’s broad hint that it might be far more efficient to first lift the very precise leaf rear sight and adjust range before firing, many of the gunners seemed content to use only the battlesight aperture, with its fixed range at about 500 yards. The guns boomed to life in fits and starts as each two man crew got their first fifty cal. experience, immediately drawing appreciative comments from those behind who were awaiting their turn. Ma Deuce is a two-fisted handful of machine gun and her noise, dust, range and hitting power combine for an awesome experience. Even those who had just come from the 40mm grenade machine gun station were impressed by the M2’s earplug-packing blast and the graceful flight of tracers followed by eruptions of flash, dust and smoke near the derelict tanks and other vehicle targets set on a ridgeline some 1000 meters away. Trying hard to remember which way to turn the T&E handwheels for the desired correction (the elevating handwheel is turned counterclockwise to raise the muzzle and putting the left thumb on the traversing handwheel and pushing it over the top moves the muzzle to the right), each crew did its best to adjust their gun so that successive bursts would walk closer and closer to the target. It doesn’t take long for each to go through his pitiful 20 rounds, and I don’t doubt that many would have pulled out their wallets to buy more M2 time if an ammo dealer had been there. (I hope I haven’t just given SecDef Cohen any ideas) Loader/observers and gunners switched places and went through the same exercise with essentially the same results. After the second set of Marine officers had their turn I was treated to an amazing sight as they all bent over and started to police up their own brass and links! Is it rude to speculate that this will probably be the only time in the rest of their service with the Corps when this will happen?

Combat Arms Track

To be fair, the Basic School curriculum is not designed to turn out fully trained Marine infantry officers, but in this case to give new lieutenants who will be going to any specialty of the Corps — including supply, administration, medical and even legal assignments — a brief introduction to combat weaponry from pistols to antitank rocket launchers. You had best believe that there is a lot more hands on time with all of the Corps’ small arms and other weaponry in store for those officers and enlisted Marines who will be assigned to the infantry and other direct combat specialties.

As tough and capable as the M2HB was and is, it can also be quite cantankerous and very picky about its mechanism. This is no weapon for those who are indifferent to maintenance or unskilled in mechanical principles. Not even John Browning could make her “idiot proof” and woe unto those who stupidly neglect to keep her clean and oiled, and who don’t regularly attend to the twin bogeymen known as headspace and timing. So, Browning made these fully adjustable in order that barrels, receivers and their working parts from many different sources could be made to work safely and efficiently. To help make sure these adjustments are precisely made anytime and anywhere, Uncle Sam provides a handy and indispensable tool with every gun. Not surprisingly, this is called the Headspace and Timing Gauge and it’s the key to avoiding a world of hurt.

Failure to properly set headspace and timing can lead to severe damage to the gun as recoiling parts batter against one another or lead to blown and separated cases with catastrophic results including having the gun literally explode in your face! Keeping this in mind, let’s take a look at the following series of photos demonstrating just exactly how these adjustments are correctly done.

Field Stripping

The M2 must, of course, be taken apart for a thorough cleaning after firing. This is no big deal since the major groups are big and easy to grab hold of and John Browning made sure that you would be able to do this with no special tools. Two very important considerations before stripping begins are to clear the gun and to make sure the bolt is fully forward. The reason for the first should be obvious, but the second ensures that the powerful driving spring rod assembly is decompressed and won’t fly out and drill a hole in your skull when removing the backplate. Don’t let your widow say I didn’t warn you.

While we take Ma Deuce apart for mandatory maintenance, let’s also examine her vital organs and marvel at the mechanical genius of John Browning.

A: The first step is always to unload and clear the gun. Raise the feed cover, retract the bolt, ensure the chamber is clear then allow the bolt to run fully forward.

B: Unscrewing the barrel requires that the barrel locking spring lug be aligned with the 3/8 in. hole in right sideplate. This is usually accomplished by placing a small link loop between the trunnion and the front of the barrel extension. However, with this particular gun, it was necessary to use the large loop. Go figure….

C: The barrel can now be unscrewed either by hand or with the help of the handy built-in wrench in the barrel carrier assembly. Notice how the barrel flares out larger just forward of the chamber providing more metal mass as a heat sink for sustained firing.

D: A side view of the backplate shows the sheet metal clip around the buffer tube sleeve that serves as the bolt latch release lock. This can be rotated up to hold the bolt latch release (center trigger between wings of the “butterfly” main trigger.

E & F: MAKE SURE THE BOLT IS FULLY FORWARD before removing the backplate. This relaxes the very powerful driving spring rod assembly so that it won’t punch a hole in you when unseated. Unlatch the backplate and lift it up and out.

G: Remove the driving spring rod by pushing in and to left, then pull the whole driving spring assembly out the rear of the receiver. This powerful mechanism drives the bolt and other recoiling parts forward to lock and fire.

H, I & J: Begin removing the bolt by first yanking the retracting slide handle rearward to free the bolt from the barrel extension. Continue pulling rearward until the bolt stud lines up with the hole on right of sideplate, allowing it to be pulled out.

K: The trigger bar is in the way of the bolt and must be pushed up as the bolt is slid rearward and out of the receiver.

L: Take care to grasp the extractor so it won’t become unseated as the bolt clears the receiver wall. Place the bolt down on its right side with the extractor up.

M & N: Begin to remove the barrel buffer and barrel extension groups by pushing a suitable small tool thru the hole in the lower rear corner of the right sideplate to unlock barrel buffer body. There’s a drift pin on the combo tool just for this purpose, but the screw end of a cleaning rod or point of a bullet works just fine. At same time, use one hand in the receiver to push the barrel extension/buffer group to the rear and remove. Keep in mind that in operation, this assembly plus the bolt and barrel are locked together on firing then recoil a short distance before unlocking. There is a lot of steel there for recoil forces of each exploding round to move.

O & P: Unlock and separate the groups by pushing the tips of the accelerator.

Q: Layout of major parts and assemblies after field stripping (top to bottom, left to right): receiver group with pintle and T&E attached, backplate, driving spring rod assembly, bolt stud, bolt, dummy cartridge, barrel buffer, barrel extension, and barrel assembly.

All Clear!

Making sure the M2 is clear after a firing session can be a bit tricky as well, particularly with a very hot gun and rounds remaining in the belt. This can lead to “cookoff” which can occur when a chambered round in an overheated barrel spontaneously detonates. It is wise to point the gun in a safe direction and allow it to thoroughly cool before attempting to unload, or use the bolt latch release lock to capture the bolt in its rear position for free circulation of air through the barrel. The first step is to unlock the feed cover and lift the belt out of the feedway. Since the gun will fire with the feed cover up it is important to keep away from the trigger butterfly until the bolt can be retracted. The gunner then pulls the bolt fully to the rear which should extract the chambered round and cause it to drop harmlessly onto the ground. The bolt can be locked rearward with the bolt latch, allowing examination of the chamber to ensure it is clear.