My Science Project
The following weapons were used in the film My Science Project:
Mike Harlan (John Stockwell), Vince Latello (Fisher Stevens) and Sherman Reardon (Raphael Sbarge) pilfer some M16 assault rifles from some Viet Cong soldiers they encounter inside the time-warped school. In a humorous sequence, unpopular nerd Sherman educates his classmates on the proper way of loading an M16.
Cobray CM203 flare launcher
Although Vinnie and Sherman's M16s are of the ordinary variety, hero Mike manages to get one with an Cobray CM203 flare launcher (standing in for the M203 grenade launcher), which is what allows him to fell the monstrous tyrannosaurus the three go up against.
Remington Model 870 Shotgun
Vinnie takes a Remington Model 870 Shotgun with folded stock from a police car when the kids first enter the school. However, it turns out not to be loaded for some reason, forcing him to instead use it as a blunt object before they get the M16s.