Jane's International Defence Review
http://www.janes.com/extracts/extract/jiw/jiw_a144.html
Oct 10, 2008
Development
The XM312 was developed as a .50 calibre variant of the XM307 Advanced Crew-Served Weapon (see separate entry).
During the course of developing the XM307 for the US Army, General Dynamics noted that the standard .50 calibre
(12.7 mm) ammunition had similar impulse characteristics to the 25 mm ammunition being developed by Alliant.
To speed gun development the firm did much of the work in the former category, since the .50 calibre ammunition
was cheap, available and well documented. Since it only required the swap-out of four components to change the
gun from one calibre to the other the Army began looking into the possibility of using a .50 calibre variant as
a training weapon to reduce ammunition costs. When the XM307 was finally killed in January 2007 the Army told
General Dynamics ATP to use the remaining funds that had been obligated on the contract to continue to development
of the .50 calibre variant, now known as the XM312. This effort was scheduled to run through the conclusion of
the System Development and Demonstration (SDD) contract in March 2008. By October 2007 three prototypes in a
Type C configuration had been built and fired. In May 2008, the Army's Armament Research and Development Center
awarded GD-ATP a USD9 million contract for further development of a lightweight .50 calibre machine gun, now
known within the firm as the Lightweight .50 Calibre Machine Gun (LW50MG). This retains most of the features of
the XM312.
The Army at present will buy new M2s and MK-19s to replace the current ones that are wearing out.
Also, the M8 may be dead but take a look at the Barrett REC7 (formerly known as the M468).