Examples from the Web for m4
He just stood up, looked over at the guy who was on the ground, pulled out his M4 and just pop pop.‘Kill Team’: The Documentary the Army Doesn’t Want You to See|Andrew Romano|July 26, 2014|DAILY BEAST
"I spent a career carrying typically either a M16, and later a M4 carbine," he said.
Brothern, "ye brothern" (M4,b), an old plural: cf. childern still in dialect use.