Here is one I saw long ago >> 20 years on TV, probably a “Creature Double Feature”.  Hippy dirtbag guy finds this alien weapon.  He puts his arm into it and has a good time blasting stuff with the laser pulse.  It may have impregnated his palm with some sort of thing (maybe a gem or a scab).  Eventually he loses his humanity to the weapon and he becomes an alien (after he finds that he can no longer remove his arm).  I remember him blasting stuff like telephone poles maybe.  Gun looked like a tube that you stuck your forearm into…poor bastard.