I imagine that some GI is in a world of trouble right about now.
Some clown lost a .45 when we were on an exercise once in Germany. The whole bn. spent days doing the double arm interval, head down, police call thing, only we were trying to police up some LT's missing .45. Never did find the damn thing, probably mashed into the mud by a tank or an APC.
Company armorer is responsible for a complete inventory every time the arms room is locked. The serial numbers will identify which arms room or storage area they came from. Someone will be court-martialed, his C.O. will probably have his career ended.