M16
From Memory Alpha, the free Star Trek reference
The M16 was a series of automatic rifles made by Colt Firearms for the United States armed forces. The M16 rifle and its variants saw extensive service with the US Armed Forces from the 1960s to the mid 21st century.
US Marine sentries used the M16A1 variant on board the aircraft carrier USS Enterprise and aimed them at Pavel Chekov during his arrest. (Star Trek IV: The Voyage Home)
