At the turn of the 20th century, before World War I, aircraft and automobiles were in their infancy. Radio was new and electricity was far from universal. Advances in technology, in particular metallurgy, were making possible new types of weapons, including the fully automatic machine gun. One basic design of 1901 still soldiers on today, outfitted with infrared lasers, night vision and thermal sights. Nearly nine decades later troops are still thumping away with the M2HB machine gun, a weapon that would be familiar to their great-grandfathers.
John Browning’s patent application, for what would later be adopted by the U.S. Army as the M1917, was filed in 1901. As World War I progressed, there was a requirement for a machine gun and cartridge capable of engaging enemy aircrft at ranges farther than the aircraft would be a threat. Winchester developed the cartridge—a scaled-up .30-06 with a .50-caliber projectile. John Browning was asked to develop a weapon to shoot it. He expeditiously scaled up the basic M1917 machine gun into what was known as the M1921, refined to be the M2 that has served for multiple generations of soldiers in myriad wars, and is at the forefront of battle in Iraq and Afghanistan as this is written.
The Soundness and the Fury
There have been few weapon designs in history that were so intrinsically sound that they could be simply scaled up into a new weapon in a major new caliber, but such a design is the Browning machine gun action. In World War II, the Japanese even scaled it up to 37mm as an aircraft cannon.
From an analytical view, the M2 is a scaled-up and slightly modified version of John Browning’s M1917 .30-caliber machine gun, even using the same timing gauges when setting up, but digesting the .50 BMG cartridge. It is a belt-fed, short-recoil-operated weapon firing from a closed bolt. Upon firing, the bolt and barrel are initially locked together during recoil and unlock after traveling rearward a short distance, allowing the bolt to continue on. The action opens, extracting both the empty and a fresh cartridge from the belt, and then downward ejecting the spent case while advancing the belt of ammunition one round. As the bolt returns, it chambers the new round just extracted from the belt. The M2HB (Heavy Barrel), the most common issue ground version, is air-cooled and cycles at 450-550 rounds per minute. This cyclic rate is generally not used, as continued fire at that rate will wear out the bore within a few thousand rounds.
The listed maximum effective range with standard ball is 1.8 kilometers (1.2 miles) when fired from the M3 tripod. As a ground-portable, crew-served piece the M2HB tips the scales at 84 pounds, with the assembled M3 tripod and T&E (Traverse and Elevation mechanism) adding an additional 44 pounds. In standard ground configuration, there are two spade hand grips on either side of a V-shaped “butterfly” trigger with a bolt release in between, just above the buffer. In normal trim there is no manual safety, though there are variants and retrofits that feature them. Most troops improvise by sliding an expended case underneath the butterfly if a safety catch is needed.
To use in full auto, the bolt release must be held down by rotating the bolt latch release lock on the buffer tube. Turning the bolt release counter clockwise unlocks the release and the gun shoots single shots with the gunner needing to depress the release to send the bolt forward for each shot. Sniping legend Carlos Hathcock famously used this feature with a Unertl-sighted M2 to make a shot at 2,286 meters in Vietnam. Over the decades the M2 has been used in many configurations, on many platforms, including fixed and flexible versions on ships and planes. It can be adapted to feed from the left or right side by changing the belt-holding and feed pawls, cartridge stops, and reversing the bolt switch. The swap can be done in minutes with no tools.
Feeding the Beast
The heart of any weapons system is its cartridge. Although the .50 BMG, 12.7x99mm, is a scaled-up .30-06 round, there is an exponential increase in its ability that has found new missions in heavy rifles for sniping, anti-materiel and long-range target use. A wide variety of projectiles have been created such as tracer, incendiary, AP (armor piercing), API (armor-piercing incendiary), and APIT (armor-piercing incendiary tracer). More recently, SLAP (Saboted Light Armor Penetrator), designated M903, and M962 SLAPT (Saboted Light Armor Penetrator Tracer) have become available.
Standard issue ball launches a 647-grain projectile from the muzzle at around 2,900 feet per second. To put this in perspective, a 1-ounce 12-gauge shotgun slug is 437 grains and moves out at around 1,300 fps. Lead core precision ammunition is heavier still, notably the Hornady A-Max at 750 grains. Projectile improvements have yielded better penetration, with the best performance coming from the saboted variants. SLAP ammunition features a heavy metal (tungsten) .30-caliber penetrator exiting at 3,985 fps and can penetrate 34 mm of hardened armor at 500 meters.
While use of the .50 is possible and legal against personnel, the round serves more efficiently against materiel and lightly armored vehicles. Hard target interdiction, such as eliminating equipment like transformers, grounded airplanes and missiles and the like at distance, and defeating armored vehicles up to the vulnerable points on main battle tanks, is a better use of the range and power this cartridge provides. Civilian competition use of the .50 BMG has provided a whole new element to long-range riflery as chronicled by the aptly named journal, Very High Power, from the Fifty Caliber Shooter’s Association. It should be noted that military use has benefited greatly from civilian competition shooting and their refinement of this venerable cartridge.
Harnessing The Heat
The first issue with any gunner’s skill is mechanical training, as gunnery concepts can’t be employed if the weapon doesn’t function. Use of the M2 is more involved because the operator is expected to adjust both headspace and timing during routine setup. While the procedure is simple, too many military personnel don’t grasp the how or why.
Headspace is the distance from the part of the chamber that stops the cartridge (datum reference) to the face of the bolt. Technically, the M2’s headspace gauge is a tapered feeler gauge only measuring the gap between the face of the bolt and the back of the barrel but, properly set, this space ensures that a cartridge will chamber without having excessive headspace. Timing is checked by a pair of parallel feeler gauges that test if the gun will only fire just as it goes into battery. These tests are simple and quick to perform but failing to do them right can be catastrophic. I have personally been involved in two investigations where undertrained personnel did it wrong and destroyed their guns.
Cookoffs, an often misunderstood problem, are of primary concern in any machine gun that fires from a closed bolt and is air-cooled like the M2. When the trigger is released a round is left in the chamber and residual heat conducts through the cartridge case. If the flash point of the propellant is eventually reached it will burn even though the primer has not been struck, thus firing the chambered round. Contrary to myth, this will not cause the machine gun to “run away” at a full cyclic rate of fire because each chambered round has to first be brought up to temperature, which takes 10 seconds or longer, and the barrel is cooling during this period. Liquid cooling and/or an open bolt design would help prevent this. However, as designed, the only solution with the M2 is effective gunnery by firing controlled bursts to prevent overheating.
With mechanical training accomplished, let’s look at employment. In many modern armies, including the United States, machine gun training has degraded to little more than equipment familiarization with engagement technique limited to direct fire on individual point targets only. Essentially, machine guns are used as big, belt-fed rifles. Here in the U.S., most machine gun ranges are of the RETS (Remote Engagement Training System) “pop up” variety and the only targets are E-type humanoid silhouettes, just like at the rifle ranges. While this has some value and should be a component of any gunnery curriculum, it is only a small part of the whole picture.
Like other support weapons, machine guns are most effective when employed to control ground. Where other small arms are primarily used to engage individual point targets the machine gunner should be able to effectively engage whole lines and/or areas of terrain without having to sight in on any individual target. Interestingly, the Commonwealth nations, notably Great Britain, Australia and Canada, seem to have best retained the lessons learned of machine gun gunnery. These countries still issue full SF (Sustained Fire) kits with machine guns that include clinometers, indirect-fire optics similar to those used on mortars, along with gunnery tables to use the gun in a variety of roles.
The M3 tripod with Traverse and Elevation mechanism is the norm for ground use with the M2. Traditionally, a simple pintle bolts the gun to the tripod; however, especially when vehicle-mounted, cradles such as the Mk 64 and Mk 93 are used. Below the receiver section the T&E connects the gun to the traverse bar of the tripod. The bar and T&E are both graduated in mils, allowing for accurate control that is both repeatable and recordable. The large hand wheel controls search (elevation) adjustments. Fine traversing adjustment is done by the smaller dial on the left and coarse correction is done by unlocking and sliding the entire mechanism on the bar.
After obtaining an initial lay of the gun, controlled adjustments can be made on the T&E mechanism without having to re-sight. If these settings are recorded on a range card, target areas and lines such as likely avenues of approach, protective lines, and obstacles can be engaged even if the gun team can’t see these pre-plotted points.
Learning the characteristics and classifications of machine gun fire allows the gun crew to effectively neutralize whole areas, dominating and denying key ground to the enemy. Covering obstacles and avenues of approach can slow down an advance or force a change of their direction of attack to suit your defense. The heavy .50 BMG offers the additional benefit of increased armor penetration, especially with SLAP ammo, and is a real threat against armored vehicles.
Historic, But Not Yet History
As with any technology, the march of progress eventually renders even the most successful designs obsolete. That a weapon first fielded nearly a century ago is still seeing front line service is a testament to its value. On the horizon are designs based on General Dynamics Armament and Technical Products’ XM307, most notably the LW50, that have been kicked around since 2000 and, according to Program Executive Office Soldier, could be in service by 2012. These designs take the the same cartridge but have half as many parts, weigh half as much, better integrate with modern sighting systems and feature an improved T&E. The claim is that these new ground mount .50’s take the same footprint as our current 7.62mm M240. However, testing has been inconclusive and no hard date for official adoption has been set. Ma Deuce may be old and worn, but she isn’t going anywhere just yet.
At the turn of the 20th century, before World War I, aircraft and automobiles…
by Tactical-Life.com / Jan 8, 2010