The Lightweight Medium Machine Gun (LWMMG) is a prototype machine gun being developed by General Dynamics Ordnance and Tactical Systems. The next generation Lightweight Medium Machine Gun (LWMMG) gives warfighters a distinct advantage in both extended and close-in fighting. Eliminating the gap between 7.62mm and .50 caliber weapons, the LWMMG utilizes the highly efficient .338 Norma Magnum cartridge to offer unmatched accuracy and lethality while extending the battlespace out to an impressive 1,700 meters.
The LWMMG is designed to fill the gap between 7.62 mm and .50 BMG machine guns. The weapon uses the .338 Norma Magnum round, giving it greater lethality and double the range of the 7.62 NATO round. The LWMMG has a rate of fire of 500 rounds per minute, an effective range of 1,700 meters (1,860 yards), and a maximum range of 5,642 meters (6,170 yards). It weighs 24 pounds, making it only slightly heavier than the M240L, and 3 lb (1.4 kg) lighter than the M240B. The .338NM bullet has over 6,300 J (4,600 ft⋅lb) of muzzle energy and is four times more powerful than the 7.62 NATO at 1,000 meters. An individual round is twice as heavy (45.5 grams compared to 24 grams), as are each belt link (8 grams compared to 4 grams).
For each weapon to fire for one minute, a belt of 500 .338NM rounds would weigh 37.6 kg (83 lb), while a belt of 800 7.62 NATO rounds would weigh 34.4 kg (76 lb). The LWMMG is operated by a gas-operated, long-stroke piston with a rotating bolt located under the barrel and fires from an open bolt. It uses “Short Recoil Impulse Averaging” technology, patented by General Dynamics and previously used on their XM806 machine gun, where the entire barrel, barrel extension, gas system, and bolt assembly recoil inside the outer housing. The LWMMG is equipped with a quick-change barrel, quad picatinny rails, collapsible stock, and can be used by dismounted troops or mounted on a platform.
While the M240 has an effective range of 1,100 m, the LWMMG fires a 300 gr (19 g) .338 bullet that can provide effective and accurate fire out to 1,700 m. General Dynamics officials say their machine gun is not meant to be a replacement for the M240, but to give the ability to put effective fire on targets at extended ranges. 100 rounds of 7.62 NATO weighs 7 lb (3.2 kg), while a 100-round box of .338 Norma Magnum weighs 9 lb (4.1 kg). The LWMMG can be mounted on an M240 mount and costs about the same. While the company is satisfied with the shorter .338NM cartridge’s performance, the gun could easily be converted to .338 Lapua Magnum. The gun’s short recoil operating system causes the barrel to reciprocate, similar to the M2 machine gun. This combined with a gas system to minimize recoil balances positive and negative recoil forces, allowing a gunner to fire a round with significantly greater energy but with the recoil profile similar to a 7.62 mm round from an M240.