In 1965, slightly modified Small Arms Ammunition Cases came into service to coincide with the adoption of the 5.56×45mm NATO M16 rifle. Four of the 20-round magazines fit snugly into the M-1956-pattern cases, but their shorter size meant a void space at the top of the case which was too small to be useful for anything else. As a result, cases were produced in 1965 and 1966, identical to the M-1956 patterns but slightly shorter. By this point the M16 had been accepted for general issue, replacing the M14s as well as M1 Garands, M1/M2 Carbines, M1918 BARs, and SMGs still in service, so the general purpose nature of these cases was no longer essential. These cases did not necessarily fully replace the M-1956 pattern but were issued alongside them.