produced 234 Stoner 63s, when production was then moved in September 1964 to the Cadillac Gage plant in Warren, Michigan. With the change in manufacturing plants, polycarbonate plastic was used for the stocks and grips instead of wood. The weapon is covered under . Trials On March 4, 1963, the Department of Defense's Advanced Research Projects Agency made the first purchase of the Stoner 63, ordering 25 units in various configurations. In August and September 1963, the Stoner 63 was sent to the Marines Corps Landing Force Development Center at Quantico for evaluation, where it made a positive impression with its light weight and high ammunition capacity; the Marines favored the rifle and light machine gun configurations. Trials were performed by the Army Materiel Command (responsible for logistical support for the Marine Corps) at their own test facilities. Many bugs affected the outcome of the Army trials of the gun: the ammunition requirements proposed were unrealistic and the weapon was expected to perform with an extremely wide range of port pressures, leaving very little power reserve with some ammunition types. For instance, the tracer ammunition used in the Stoner 63 was of such low pressure that it even failed to function reliably in the M16. These factors severely affected the weapon's reliability. After several months of testing, the Stoner 63 system was ultimately deemed to be unacceptable for service use. The Army submitted recommendations for improvements to the design—these included a stainless steel gas cylinder, a two-position fire selector with separate safety, ejection port dust covers and modifications to the belt feed mechanism. The upgrades resulted in the improved Stoner 63A, which began production in 1966. Only about 2,000 examples of the initial version were manufactured before the transition to the model 63A. XM207 upgrades From 1969 to 1971 Cadillac Gage Co initiated a program to upgrade the Stoner 63 light machine gun due to Marine Corps interest. They were given one last chance to make design improvements and have a final test by the Army Materiel Command. Several changes were made to the weapon, soon to be designated "XM207 Light Machine Gun". Misfires, high cyclic rates, jams and link separations were among the issues to be resolved. The 63A used a stack of Belleville spring washers to absorb some of the shock and bounce when the firing pin struck the primer. By changing the configuration of the washers, a