XM312 Advanced Crew Served Weapon
XM307K50 Advanced Crew Served Weapon
12.7mm Weapon System

The original plans to replace obsolete, but numerous .50 caliber (12.7mm) Browning M2HB heavy machine guns in the US service listed the Objective Crew Served Weapon (OSCW) as a successor to the Browning machine gun. By 2000, the design of the M2 was over 80 years old. Delays in the development of the highly expensive and sophisticated OCSW led to the conclusion that the US forces did need something new, and at least as effective as old weapon, but immediately.

In 2000, the 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 baseline OSCW, which became designated as the XM307 in FY03, used .50 caliber impulse loads, so General Dynamics Armament and Technical Products decided to develop a 12.7mm/.50 caliber derivate of the existing weapon. The .50 caliber variant, first presented to the Program Executive Office Solider in August 2003, was initially termed the XM307K50. In FY04, the designation for the derivative was changed to XM312. The XM312 could be readily converted to the 25mm XM307 in 2-4 minutes, by swapping out 4 unique parts.

The XM312 lightweight heavy machine gun, while based on the 25mm XM307, did not feature that weapon's comprehensive and expensive explosive ammunition and fire control, and was much cheaper and could be finalized much faster. General Dynamics Armament and Technical Products was the prime contractor with total system integration. The XM312 was initially to be developed as part of the XM307 program being managed by the Joint Services Small Arms Program Office located at the US Army Armament Research, Development and Engineering Center, Picatinny Arsenal, New Jersey. The XM307 program transitioned to PM Crew Served Weapons management in the fourth quarter of 2003.

By 2004, the XM312 featured less than 1.2 miles targeting, with a weight of 29.3 pounds (with only iron sights). The weapon utilized the same lightweight tripod and innovative T&E as the XM307. The weapon's length was 53 inches overall and it could achieve a sustained fire rate of 40 rounds per minute, the same as .50 caliber M2 machine gun. The cyclic rate of fire was set at 220-250 rounds per minute. The weapon's recoil force was 150-250 pounds. A muzzle velocity of 2,760 feet per second using M33 ball ammunition.

The XM312 reduced overall cost to the XM307 reliability program. In using .50 caliber ammunition the weapon greatly increased overall system reliability. While only 4 parts were unqiue to the XM312, a fifth part was also modified and made common to both the XM307 and XM312. The weapons had a 95 percent commonality in parts. The weapon had the same impulse and breech loads as the XM307 and allowed for the reaching of a higher reliability level for the XM307 program as a whole. The accuracy and lightweight characteristics of the 25mm XM307 were conversely leveraged to provide a highly accurate lightweight .50 caliber weapon.

As of early 2004, the Advanced Crew Served Weapon had met all Advanced Technology Demonstration exit criteria, and had entered the System Development and Demonstration (SDD) phase.

The ACSW system was selected to serve as the Common Close Support Weapon (CCSW) system for the Future Combat Systems (FCS) Unit of Action in FY04. The selection of the ACSW for the FCS CCSW program led to interest in the system for the Stryker series of vehicles the in development. A Remote Operations Kit (ROK) was developed for the XM312 as part of its potential integration in both instances. Phase 1 of the intregration of the ACSW family onto the Stryker remote weapon station (RWS) was accomplished in fourth quarter 2004. The XM312 was integrated onto the Kongsberg Block 1 RWS. The result was successful integration, operation, targeting, and firing.

The ROK was functional for use on either the 25mm and .50 caliber weapon. It required external power, and included: Remote charger and sensor; remote safe/arm and Sensor; misfire sensor; and charged/uncharged Sensor. The ROK was mounted on the gun cradle, which would facilitate dismounting for tripod use.

With the termination of the manned components of the FCS program in 2008, the decision was made to effectively shelve the ACSW program. The experience gained in the development of an advanced lightweight .50 caliber machine gun to replace the existing .50 caliber M2 machine gun was spiraled out into the development of what became the XM806 machine gun.