FN Herstal’s M3M Pedestal Mount .50 BMG Machine Gun

By Charles Cutshaw

The Browning .50 Caliber machine gun has been in production in one version or another since the 1920’s and continues in production on a worldwide basis today without any sign of coming to an end. John Browning’s basic design is one of those that is simply too good to die. Since its inception, the basic .50 Browning machine gun has been manufactured in M2, AN-M3 and other variants that essentially were modifications of the original Browning design. The latter gun was an effort undertaken by the US during World War II to provide an aircraft gun that not only was lighter, but fired at a higher cyclic rate than the standard AN-M2. The M3 fired at a cyclic rate of approximately 1,200 rounds per minute (rd/min), but was plagued with sear breakages, cracked bolts and other malfunctions and while the gun was standardized in 1943, only about 2,400 were manufactured by the war’s end. The US Military modified the M3 in the late 1940s in an attempt to increase reliability, but the M3 never lived up to its expectations and it was eventually dropped from the US inventory in the early 1950s.

Meantime, however, FN Herstal undertook production of the M3 and steadily improved its performance and reliability, first by changing the basic functioning of the gun from closed bolt to open bolt operation. FN also undertook “reindustrializing” the basic design to increase reliability and longevity. These reindustrializing efforts included an examination of the entire AN- M3 design with a focus on materials, heat treatments, tolerances and finishes. By modifying and changing these functional areas as necessary, FN Herstal’s engineers were able to turn the AN-M3 design into the M3P, whose mean rounds between failures (MRBF) is presently over 5,000. This gun initially was produced for mounting in an external pod on fixed wing aircraft and helicopters. The M3P is widely employed by the world’s military forces, including the United States, where it is used in the AN/TWQ-1 Avenger air defense system, mounted coaxially with the Avenger’s Stinger missile launchers. The M3P is also deployed on some UH-60 Blackhawk helicopters in external pod mounts.

With the success of the M3P, the possibility of adapting the gun for other applications became obvious. FN Herstal engineers undertook the challenge by first changing the basic functioning of the gun from closed to open bolt operation. This helps in cooling and prevention of “cook-offs,” a critical concern in machine guns with a high cyclic rate of fire. They then adapted the gun to internal and external flexible “soft” mounts for helicopters and fixed wing aircraft and more recently, for application to land vehicle pedestal mounts where the M3M’s high rate of fire increases its effectiveness over the traditional “Ma Deuce” vehicle mounts. They also eliminated the requirement for timing adjustments. There currently are no plans to adapt the M3M to a ground mount configuration. This is due partially to the fact that the M3M’s high rate of fire would probably create ammunition supply problems in many ground situations, as the M3M fires at over twice the cyclic rate of the basic ground mount M2 HB machine gun. For vehicles, however, the M3M offers decided advantages over the older design, primarily because of its high rate of fire that makes it more effective against a variety of targets, including light armored fighting vehicles, field fortifications, helicopters, fixed wing aircraft and small patrol boats.

As a flexible pedestal mounted heavy machine gun, the M3M is well suited to either helicopter or ground vehicle mounting. The pedestal adapter consists of a soft mount that attenuates felt recoil, while at the same time placing the gun in such a well-balanced position that the gunner has almost effortless control. A spring balances the gun when it reaches approximately -30 degrees deflection. Stops can be incorporated to limit the traverse and elevation of the gun depending upon the vehicle or aircraft on which it is installed. The effort to cock the M3M has been significantly reduced over that of its predecessors by incorporating a lever that provides a mechanical advantage when pulling the charging handle to the rear. The firing handles are located on the pintle mount, rather than on the gun, for better control. There are three types of sights available: Open ring sights, optical sights and laser sights. The gun’s safety mechanism positively prevents accidental or negligent discharges and at the same time, when placed in the “fire” position, prevents the feed cover from being opened.

The M3M fires from the open bolt and is fed either from a 100 round box mounted on the pintle or from a 600 round box mounted on the aircraft or vehicle floor. The barrel is hard chrome plated with stellite added for longevity. In fact, the gun is capable of firing an uninterrupted 600 round burst without damage to the gun or barrel. Since the 100 and 600 round ammunition boxes would quickly be exhausted by the M3M due to its high rate of fire, the 600 round ammunition boxes are designed to be “nested” to provide 1,200 rounds of ready ammunition. Spent cases are ejected down and slightly forward, while up to 600 links are collected in a container beside the gun. The M3M can be adapted for either right or left hand feed and can fire any type of .50 BMG ammunition. When using FN’s .50 BMG armor piercing explosive incendiary (APEI) ammunition, the M3M can defeat 10mm of rolled homogenous armor (RHA) at 1,000 meters. Maintenance is straightforward and conventional. The only regularly scheduled maintenance requirement is that a few minor M3M components are recommended for replacement every 2,500 rounds in order to ensure optimal reliability.

In addition to manufacturing new M3M machine guns, FN has the capability to convert customer’s older M2 or M3 guns to M3M configuration. FN can also adapt the M3M to virtually any helicopter or ground vehicle. With its high rate of fire, soft recoil and levels of reliability, the M3M heavy machine gun is ideally suited for helicopters, for pedestal mounting on light ground vehicles and on light patrol vessels. It appears to be an excellent weapon for special operations, for drug interdiction missions of all types, for patrol vehicles and boats and for patrol helicopters.

This article first appeared in Small Arms Review V4N12 (September 2001)
and was posted online on April 14, 2014


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