GD Lightweight Medium Machine Gun / LWMMG(photo: GD ATP)


GD Lightweight Medium Machine Gun / LWMMG on M192 tripod (photo: Tony Williams)


GD Lightweight Medium Machine Gun / LWMMG (photo: GD ATP)



.338 Norma Magnum / 8.6×64


10.9 kg / 24 lbs (gun with bipod) + 5.2 kg / 11.5 lbs (M192 tripod)

Overall length

1244 mm / 49”

Barrel length

609 mm / 24”

Cyclic rate of fire

500 rounds per minute

Feed and capacity



Lightweight Medium Machine Gun (LWMMG) is the new, prototype weapon developed by US defense industry giant General Dynamics. LWMMG was first displayed to industry specialists during NDIA conference in May, 2012. It is yet to be seen if the weapon will live to expectations, and it seems that it has a long way forward for possible adoption.

The concept of the Lightweight Medium Machine Gun is apparently based on the current US Army doctrine for “overmatching capabilities”, requiring new weapons to provide more effect than weapons of its adversaries. In this particular case, LWMMG is to overmatch small arms (7,62mm rifles and machine gun), widely employed by insurgents in Iraq and Afghanistan. Until now, small units of US Armed forces had small arms (rifles and general purpose machine guns) with more or less matching capabilities in terms of range and lethality (hitting power).

338 Norma Magnum cartridge is a recent development. It has evolved from .338 Lapua Magnum cartridge by shortening the case and slightly altering its shape, to ensure same overall length as .338LM with longer heavier bullets with outstanding ballistic properties. In its basic form, .338 NM cartridge, when fired from LWMMG, launches very low drag Sierra MatchKing bullet weighting 19.44 gram (300 grains) at 808 m/s (2650 fps), with muzzle energy in excess of 6300 Joules (4600 ft-lbs).

The LWMMG offers noticeable increase in terms of range (from about 800 meters for 7,62mm GPMG such as M240 or PKM up to 1700 meters for LWMMG) and lethality. Terminal energy of the bullet at 1000 meters range for .338NM bullet fired from LWMMG is almost 4 times higher than energy of the 7,62mm bullet fired from M240. It must be noted that Lightweight Medium Machine Gun (LWMMG) is intended for many different applications, including use by dismounted / foot soldiers. The gun itself is relatively light, and actually is lighter than 7,62mm M240B machine gun by about 3 pounds / 1.3 kg. The key issue is ammunition, as .338NM cartridge is twice as heavy compared to 7,62×51 NATO cartridge (45,5 g / 702 grs for .338 compared to 24 g / 370 grs for 7,62). Links for LWMMG also are twice as heavy compared to standard M13 7,62 NATO links (8 gram vs. 4 gram). To make a comparison, .338 LWMMG with one minute worth of ammo for sustained fire (500 rounds in belts) has total weight of 37,6 kg, while M240B with one minute worth of ammo (800 rounds in belts) has total weight of 34,4 kg.

Lightweight Medium Machine Gun (LWMMG) is gas operated weapon that fires from open bolt. It employs more or less conventional rotary bolt locking and long stroke gas piston, located below the barrel. Air-cooled barrel can be quickly removed for replacement or maintenance.

The key to light weight and relatively moderate peak recoil of the LWMMG is patented “Short Recoil Impulse Averaging” technology, which is an adaptation of the old “differential firing” principle, previously used in the XM806 .50 caliber machine gun, also developed by GD. In this system, entire barrel / barrel extension / gas system / bolt assembly is allowed to recoil inside the outer housing. The bolt group cycles inside the barrel extension in a usual manner, feeding, firing, extracting and ejecting rounds, while entire assembly slides back and forth, noticeably decreasing peak recoil forces. Another feature of this system is that mechanism is timed to fire each round while the recoiling group is still moving forward, further decreasing peak recoil.

The LWMMG is a belt-fed weapon, with left-hand side feed. It uses specially designed disintegrating metallic belt with steel links similar in design to US M13 7,62mm links, but made appropriately bigger to accept larger .338NM cartridge. Feed is of push-through type.

Existing prototypes of the LWMMG are fitted with pistol grip and trigger below the receiver, and telescoping shoulder stock at its rear end. Gun can be fired from integral folding bipod, from M192 tripod (originally developed for M240 and M249 machine guns), and from variety of vehicle mounts. Sighting means are provided via NATO-standard (Picatinny) accessory rail, which can accommodate wide variety of day- and night-time sights, depending on the upcoming mission profile.

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