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.