XM312 large-caliber machine gun (US Gun Reviews)

The XM312 is a machine gun based on the 25mm XM307 automatic grenade launcher and is reserved for the .50 BMG cartridge.

XM312 large-caliber machine gun (USA Gun Reviews)

MilitaryEzyInfo.com – In 2002 the US Army received from Primex Technologies for testing the first prototypes of 25 mm XM 307 OCSW (Objective crew-served weapon) – a virtually automatic grenade launcher, allowing target engagement with high-explosive fragmentation rounds with programmable remote fuzes. This lightweight and highly mobile weapon, equipped with a powerful sighting system, was to replace both the Mk 19 automatic grenade launcher and the Browning M2 heavy machine gun in the US Army’s weapons system.

However, XM 307 design and development proved to be long and complicated, and the system itself appeared to be quite expensive. This considerably slowed down its adoption.

At the same time, the rearmament of the US Army became necessary due to the serious escalation of tensions, primarily in the Middle East region. Around 2000 it was decided to create a new heavy machine gun based on the HM 307, which could temporarily replace the OCSW system until the latter was finalized.

The development of the gun, designated HM 312 (M 312 after adoption), is carried out by the General Dynamics Advanced Technology Products division of the U.S. General Dynamics Corporation (according to some reports, the development of the 25 mm KM 307 system was also transferred to it) in conjunction with AAI Corp.

At approximately the same time the LMGA (Lightweight Machine Gun and Ammunition) program was approved, and the XM 312 was included in this program. The program documented all previous requirements for the new weapon and was designed to reduce weight by 35% compared to current weapon models, with more than 40% reduction in ammunition weight. The program was also intended to significantly improve weapon ergonomics and reduce training and maintenance costs.

In 2004. “General Dynamics Advanced Technology and AAI Corp. presented the military with a prototype machine gun for initial testing. The military commission in charge of the LMGA program planned to complete the entire HM 312 test program in nine months, with all activities estimated at $24 million to $32 million. The first large-caliber machine guns of the production run were to be delivered to the Army in 2006.

The XM 312 machine gun and XM 307 grenade launcher are made from a large number of standardized parts, including the tripod, weapon casing, sights, trigger mechanism, and pointing system. All of these parts give both components of the OCSW system an identical, easily recognized appearance. In essence, the only original part of the XM 312 was the gun body itself, “hidden” under the cover, so the only identifiable features are the barrel length and the shape of the muzzle brake. Another interesting feature of the XM 312 was that it could be quickly converted into a 25mm XM 307 grenade launcher. This upgrade takes less than 5 minutes and requires only a total of 6 parts.

General Dynamics’ specialists did a great job in reducing the weight. XM 312 has mass-size specifications comparable to those of some 7.62 mm machine guns in an infantry machine gun. This resulted in high mobility of the weapon and allowed for the reduction of the crew to two men, while the ammunition from Browning’s large-caliber machine gun, contrary to the original plans, remained still powerful. With the reduced weight, this threatened to seriously compromise the accuracy of the weapon, but it did not.

The reason is that the recoil is considerably reduced due to the special operating scheme of the KM 307, which is based on the ejection of the moving parts at the moment of firing. Basically, the weapon is based on the principle of constant force on the buttstock, which was proposed by Australian inventor Russell Robinson more than half a century ago, at the height of the Second World War. At that time Robinson’s experimental machine guns did not attract the attention of the military, but now it seems that old ideas are beginning to be revived in a more perfect form. But some things were different, and the XM 312 had to be improved. Using a two-fold roll-out scheme compared to the Browning large-caliber machine gun reduced the velocity of the weapon.

However, the gun’s rate of fire is said to be unaffected by this, as in practice the Browning did not fire more than 80-100 rounds/minute. But it provided better conditions for barrel cooling and automatic fire control.

This rate of fire was quite sufficient to fight ground targets (infantry inside shelters and houses, cars, etc.), but the KM 312 was no longer good enough for a small anti-aircraft defense. However, the US tactics for the ground attack suggest that the US Army has overwhelming air superiority, so the infantry XM 312 seems to be a fairly effective weapon. But installing the XM 312 on fast-moving combat vehicles (jeeps, infantry fighting vehicles, tanks, and especially helicopters) is also unlikely.

So, there is a big question, if the US Army needs such a highly specialized and very expensive weapon, when they have a proven and relatively cheap Browning – too heavy, but versatile and rapid-firing.