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.
In 1965, Small Arms Ammunition Cases that had been slightly modified entered service with the introduction of the 5.56×45mm NATO M16 rifle. Four out of twenty-round magazines fit into the cases but left a top space too small for any other use.