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Weapon Name- .338 Lapua Machine Gun
Round Type- .338 Lapua Caseless
Over-all length- 48 inches
Barrel length- 24 inches
Weight- 24 lb
Rate of Fire- 600 RPM
Feed Mechanism- Belt
Round Capacity- 100+
Effective Range- 1500 meters
Range- 2500 meters
Accuracy- 1 MOA
Accessories- Picatinny Rails
Quick switch firing mechanism- N/A
Scope/Sights- Picatinny Rails
Muzzle Velocity- 19.44 g (300 gr) Lapua Scenar GB528 VLD, 855 m/s (2,800 ft/s) 7,100 J (5,260 ft·lbf)
Firing System- "Short Recoil Impulse Averaging" long stroke gas piston
Miscellaneous/electronic information- A slightly modified caseless .338 Lapua Magnum variant of the LWMMG, a gas-operated, long-stroke piston opent bolt machine gun with a rotating bolt located under the barrel. It uses “Short Recoil Impulse Averaging” technology, similar to the XM806 machine gun, where the entire barrel, barrel extension, gas system, and bolt assembly recoil inside the outer housing.




The LWMMG is designed to fill the gap between 7.62 mm NATO and .50 BMG machine guns. The weapon uses the .338 Lapua Magnum round, giving it greater lethality and double the range of the 7.62 NATO round. This is in contrast to the original LWMMG which utilized the .338 Norma, which was utilized because the case shape allowed the weapon to be more ideally fed in automatic weapons. Because of the use of caseless variants of the .338 lapua, the .338 lapua's shape has been changed to more ideally feed in to machine guns, and thus this discrepancy is no longer a major factor in the weapon choice. Being a more commonly used cartridge and more powerful, the .338 Lapua, which is very similar in performance to the .338 Norma, was chosen instead. 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), although practical purposes restrict the weapon to under 2500 meters. It weighs 24 pounds, making it only slightly heavier than the M240L, and 3 lb (1.4 kg) lighter than the M240B. The .338 Lapua bullet has approximately 7,100 joules (5,260 ft·lb) of muzzle energy and is twice as powerful as the 7.62mm NATO at the muzzle, and four times more powerful than at 1,000 meters. The purpose of the weapon is to provide the same long range target acquisition and antipersonnel capabilities of the .50 caliber machine gun, while still being practical usable by infantry units. As the combined weight of the weapon and ammunition of a .50 caliber machine gun is far too heavy for an average infantry team to carry (a .50 caliber machine gun being 80 pounds alone, and the ammunition approximately 3 times heavier), soldiers have had no middle ground between the .50 caliber machine gun and 7.62mm nato. The .338 lapua has almost the same range as the .50 caliber round (against soft targets), despite being substantially smaller, lighter, and with less recoil, allowing it to be used in smaller weapons. The .338 lapua machine gun can also be fired at the shoulder, making it usable by only one soldier and when not set up on a tripod (unlike the .50 caliber machine gun).

An individual ,338 Lapua caseless round would be almost twice as heavy as the .308 (25.5 grams compared to 14.3 grams), as are each belt link (1 grams compared to 2 grams). A belt of 500 rounds would be approximately 30.25 pounds, compared to 17 pounds for the 7.62mm NATO. In comparison to the non caseless variants, an individual round is twice as heavy as well (45.5 grams compared to 24 grams), as are each belt link (8 grams compared to 4 grams), with 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). It's clear the caseless rounds allow for substantially larger round counts, or lighter carry loads. The .338 Lapua's ballistics] allow it a much farther engagement distance than a standard 7.62mm NATO round, breaking the sound barrier at 1900 yards, and possessing 1000 joules at 2000 yards, and 500 joules at 4000 yards. The round is also able to penetrate lightly armored vehicles that the 7.62mm NATO is not, as well as standard body armor worn by soldier.

The LWMMG is seen as a bridge between 7.62 NATO and .50 BMG machine guns. 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. The LWMMG can be mounted on an M240 mount and has a similar cost, which makes it capable of being used in this role when needed. 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. 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 .50 caliber machine gun is more powerful, it is impossible for an average weapons team or infantry machine gunner to utilize one, being a nearly 300 pound package, compared to 100 pounds for the .338 lapua machine gun. Furthermore the .50 caliber machine gun must be set up on a tripod to fire and cannot be easily carried or used by a single soldier, meaning that in an emergency it must be abandoned rather than double as a squad automatic weapon (SAW). The lack of versatility and extreme weight makes the .50 caliber round unviable, while the short range of the M240 makes the squad vulnerable to enemy fire beyond 850 meters. This makes the far more accurate and aerodynamically efficient .338 Lapua an effective midrange option, lacking the power of the .50 caliber round, but still being powerful enough for anti personnel purposes, not only having more than enough stopping power against human targets, but also capable of penetrating body armor and lightly armored vehicles at a distance.

General Dynamics first realized the capability gap being experienced by U.S. forces in Afghanistan around 2010. In many cases, troops were on low ground and being engaged by PKM machine gun fire from the high ground, forcing them to return fire from where they were instead of being able to seek a better position. The M2 .50-caliber machine gun is too heavy for use by dismounted patrols, and rounds from an M240 begin to drift off target at 800 meters, especially when shooting upwards. At closer ranges, an M240 is accurate but does not have enough penetrating power against hard structures. The Precision Sniper Rifle competition going on at that time also showed the U.S. military was interested in infantry weapons with a 1,500-meter range. At 1,000 yd (914 m), the 7.62 NATO's velocity drops to about 1,000 ft/s (300 m/s); at that range, the .338 LM travels at 2,000 ft/s (610 m/s) and out to 1,100 yd (1,006 m), the round is capable of defeating Level III armor. A machine gun was then designed around the concept with Short Recoil Impulse Averaging technology, uses available subsystem components to keep cost down, and has a broad view 6-power scope to enable point target engagement out to 1,000-1,200 meters

An improved LWMMG was displayed at AUSA 2014 with its weight decreased to 22 lb (10.0 kg). Previously, the gun underwent a firing demonstration with special operations elements at Camp Roberts, California. When firing from a bipod, the gunners were able to fire directly and hit targets as far out as 1,950 m (2,133 yd). At that range, a .50 caliber machine gun is designed to be an area weapon and could only fire accurately with single shots, while the LWMMG can maintain accurate automatic fire beyond what the .50 Cal is capable of. This showed the weapon's significance of hitting targets at longer ranges than what an M240 can do that would require the use of a vehicle-mounted .50 caliber weapon. A demonstration firing of the LWMMG is expected to take place in late October at Fort Benning, Georgia. All variants of the weapon can also fire an explosive variant of the .338 lapua, which while possessing less kinetic energy than the .50 cal, allows it to penetrate the same barriers and deliver roughly the same damage as a standard .50 caliber round.