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FN® M3M (GAU-21)

Available for military sales only.

The FN® M3M (GAU-21) is a .50 caliber (12.7x99mm) single barrel rapid-fire machine gun suitable for rotary-wing aircraft applications providing defensive firepower ranging out to nearly 2000 meters. The FN M3M™ was designated by the U.S. Navy as the GAU-21 in 2004. The U.S. D.o.D. has authorized the use of the GAU-21 for all branches of service, and it is currently in operation on multiple rotary-wing platforms of the US Navy, US Marine Corps, and the US Air Force. An evolution of the M3 .50-caliber heavy machine gun, it produces a blistering 1,100 rounds per minute cyclic rate of fire through the use of open-bolt operation and a dual recoil buffer system. Operating independent of either electrical or hydraulic power sources, the FN M3M™/GAU-21’s unique soft mount system enhances weapon accuracy and minimizes the firing vibration transmitted to the airframe.


FN Herstal has been awarded a sole-source U.S. Navy contract to produce the FN® M3M .50-caliber machine guns under the Gun, Aircraft, Unit-21 (GAU-21) designation for Navy and Marine Corps rotary-wing assault aircraft.

Military pricing on request.

*Product follows USA specifications
*Military products available to U.S. sales only


  • CALIBER: 50 BMG (12.7x99mm) NATO
  • OPERATION: Short-recoil
  • CAPACITY: 100 - 600 Rd.
  • WEIGHT: 81.6 lb.
  • RATE OF FIRE: 950 - 1,100 RPM

General Specs

Full auto

Open-bolt design


Solid steel frame for durability

Open-bolt operation limits heat build-up to reduce potential of cook-off

Dual buffer system provides twice the rate of fire as the M2 system

Recoil buffer system for increased accuracy with reduced wear and vibration


Hammer-forged steel

Useful barrel life of 10,000 rounds for simplified logistics and service requirements

Enhanced flash hider offers reduced firing signature to increase compatibility with current night vision equipment

Perforated barrel jacket for improved cooling and longer barrel life


Mount provides optimal field of fire with the aircraft centerline for wider target coverage

Mount provides -70 degrees maximum depression angle for wider target coverage

Soft mount reduces recoil for both operator and airframe


Vibration isolated dual spade grips for enhanced control in burst and sustained fire

Manual recocking lever reduces cocking effort required

MIL -STD 1913 mount for sighting and target designation systems


NATO standard disintegrating link belt feed for added reliability

Flexible metal ammunition belt guide system reduces misfeeds

Fired link collection system for added aircraft and aircrew safety