I'm looking for a movie (Circa early 80s, maybe late 70s) about a teenager who finds a laser pistol and succumbs to "Power corrupts" eventually going on a killing spree. I remember that the gun required an amulet than eventually began to change the teen. I think the teen was one of those kids that was made fun of and thus used the gun for retribution. I also remember the film not being very good so I've not had a lot of luck with Google on this one.
It sounds like Laserblast (1978):
An edited version was shown on MST3K.