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M312 .50-Caliber (12.7mm) Machine Gun

Currently being developed by General Dynamics Armament and Technical Products (GDATP), the XM312 is a lightweight, portable 12.7mm machine gun that provides increased accuracy, effectiveness, and lethality over current heavy machine guns. GDATP is the prime contractor with total system integration. This new weapon (XM312) offers a significant difference from its predecessor in that the gun and tripod weighs slightly more than 42 pounds compared to the BMG that has a total weight of 128 pounds and can accept belt-fed ammo from either the left or right. In the XM312 the gun barrel moves and not the bolt, reducing the recoil of the weapon, and with the slower rate of fire the gun can function for an indefinite period without damage and does not require headspace or timing adjustments. The 312 is nine times more accurate than the M2.

The M307 system can be quickly and easily converted to a 12.7mm / .50-caliber machine gun. The XM312 can be converted from a .50-caliber machine gun to the M307 firing 25mm airburst ammunition in two minutes by changing four parts. Being able to convert the 312 to 307 while in field will give the front-line Soldier flexibility in choosing weapons to meet the mission.

The XM312 shoots, handles and maintains like a light machine gun. Firers are amazed at both the accuracy and steadiness of the XM312. It has a sight, and it doesn’t move much because there isn’t much kick, so you can keep your eye right on the crosshairs. It is a very easy weapon to shoot. The ability to lay the first round on target is impressive. It would be very beneficial downrange. There’s zero time for the bad guy to see what’s going on. That also means a more optimal use of ammunition. It conserves a lot of rounds because of the accuracy. Shooters would be able to hit the target every time.

The XM312's advancement over current .50 caliber (12.7mm) machine guns is achieved by a significant reduction in weight, which contributes to the weapon's ability to be easily transported in small soldier units, and recoil mitigation technology, which increases ground-mounted accuracy. Future utilization of magnification and night-vision sights will allow for effective use at ranges up to 2,000 meters. Another key feature of the XM312 is its ability to be quickly converted to a 25mm grenade machine gun weapon system. The modification takes less than 5 minutes and involves 6 or less parts. By producing a family of weapons utilizing a common platform, GDATP has reduced user cost, provided a diverse weapon to meet situational needs and increased mission-critical space.

The original plans to replace obsolete, but numerous .50 caliber (12.7mm) Browning M2HB heavy machine guns in the US service listed the 25mm Xm307 OCSW weapon as a successor to the 80+ years old Browning. But the delays in the development of the highly expensive and sophisticated OCSW led to the conclusion that the US Forces do need something new, and at least as effective as old "Ma Deuce" (M2HB) right now. So in 2000 US military requested a lightweight, .50 caliber machine gun to supplement old M2HB until the arrival of the much more effective 25mm XM307 OCSW system. The XM312 "lightweight heavy machine gun" is based on the 25mm XM307, but without its comprehensive and expensive explosive ammo and fire control it is much cheaper and could be finalized much faster.

The XM312 will be one of the lightest (if not lightest of all) .50 caliber (12.7mm) machine guns on the market. This advantage, which will make it two-men portable, comes at the cost of decreased cyclic rate of fire, which is more than 2 times lower, than on other .50 caliber guns. This will made this gun strictly anti-ground weapon, because this low rate of fire will made it ineffective against fast-moving targets like helicopters and low-flying aircrafts. The practical rate of fire, however, is quoted to be no less than of M2HB, around 40 rounds per minute. XM312 also should be no less (if not more) accurate than the M2HB.

The design of the XM312 is based on the recoil-reducing action developed for 25mm XM307 OCSW. The barrel is locked by the conventional rotating bolt, which is operated by more or less conventional gas system. The bolt group mover within the barrel extension, which, along with the barrel and gas system, can recoil inside the gun housing. The XM312 fires from the open bolt, and at the moment of fire the recoiling group (barrel, barrel extension, gas system and gas drive) is in its rearmost position. When gun is fired, special spring first begin to move recoiling group forward. Then, bolt is released, it strips the cartridge into the barrel, locks it and cartridge is fired, while recoiling group is still on the move forward. The recoil of the shot first has to overcome the inertia of the recoiling group, and only then group began to recoil back, compressing the return spring. At the same time gas drive unlocks the bolt, and retracts it within the barrel extension, extracting and ejecting a fired case. This somewhat complicated design results in significantly reduced recoil, and in conjunction with muzzle brake, in lightweight, but stable construction. The price of this reduction in recoil is complicated (and expensive) construction and low cyclic rate of fire. The feed is using same old metallic belts, and XM312 can be fed from either side, alternatively.

GDATP is developing the XM312 weapon and mount as part of the XM307 program being managed by the Joint Services Small Arms Program Office located at the U.S. Army Armament Research, Development and Engineering Center, Picatinny Arsenal, NJ. The XM307 program transitioned to PM Crew Served Weapons management in the fourth quarter of 2003.

Common Close Support Weapon (CCSW)

The XM312 is the foundation for the Future Combat System's Common Close Support Weapon system providing a low risk approach and easy growth potential to 25mm air bursting munitions. This spiral development approach provides tremendous flexibility for the Transformation campaign. The XM312 and/or the XM307 are currently planned for mounting on seven of the eight vehicles requiring close support offensive and defensive capabilities. Common Close Support Weapon applications include: MCS, NLOS-C, NLOS-M, FRMV, R&SV, C2V, and ARV-A(L).

In support of Annexes D, G and I of the FCS ORD dated 15 April 2003 the XM307 Advanced Crew Served Weapon will be developed as the Common Close Support Weapon for potentially nine FCS vehicle variants. The XM307, ACSW, is a core essential system for FCS Increment 1. The Acquisition Strategy and Acquisition Plan were approved by the AAE on 30 Dec 2003. A J&A has been submitted to the Army Acquisition Executive for approval to award the SDD contract to the original weapon system developer. The PM will utilize Alpha negotiations to award a Cost Plus Award Fee contract. Cost as an Independent Variable and Design to Unit Cost will be applied. Supportability will be addressed (at the beginning and) throughout the program.

By replacing the 75-year-old M2 machine gun the Army achieves significant reductions in weight and recoil force. The XM312 weighs approximately one third the weight of the M2 and imparts only one quarter of the recoil. This lighter weight permits easy dismount and ground transportability when necessary and the reduced recoil will lead to greater lethality through increase first burst accuracy.

Common Close Support Weapon (CCSW) Weapons Trade Study participants included USAIC, UAMBL, LSI, VIs, PM-Lethality, PM-SW, PM-MAS, AMSAA, ARL. Eight weapons were traded: M240, MK19, MK47, M2, XM312K50 (XM312), XM307, M230, and RMK30. Trade criteria included: Lethality; Weapon and Ammunition life cycle costs; Risk; and Integration issues. The study found the XM307 was not the best in any one category, but it was selected as the weapon of choice with all aspects considered. The XM307/XM307K50 (XM312) among the lightest weight and smallest volume. The XM307 was among the most lethal, and was rated low risk w/ XM307K50 (XM312) and off-the-shelf ammunition as a fallback.

PM-SW is to develop the XM307 & XM307K50 (XM312) weapons, the family of 25mm ammunition, the dual feed module, and the remote sensor package for remote operations. GDLS is to develop the weapon mount, ammunition feed system, and remote weapon charger. UDLP is to develop the fire control (XM307 FC not utilized), the stabilization package, and conduct overall integration as a system.

The Remote Operations Kit is functional for 25mm and .50 cal use. It requires external power, and includes: Remote Charger & Sensor; Remote Safe/Arm & Sensor; Misfire Sensor; and Charged/Uncharged Sensor. The ROK is mounted on Gun Cradle, which Will facilitate dismounting f/ Tripod use.

The Dual Feed Module Concept is for 25mm use only. It is remotely operable, and must be compact and lightweight. It provides first round response selection, and requires external power. It may require magazine “booster”.

As of early 2004 the Advanced Crew Served Weapon (XM307) had met all ATD exit criteria, and had entered System Development & Demonstration.