Well done on the review for Laserblast! There is another movie I've seen that is similar . It's about a boy who finds a case (or futuristic backpack) with an alien pistol of immense power inside. I think the gun has some kind of cord coming from the base of the handle going into the pack. He's abused by his father who, if I remember correctly comes at him with a baseball bat and the boy fries him. He then goes on the run. If I also remember correctly he gets together with a girl that he's had his eye on and they steal a car and end up getting into serious trouble with the law. I believe they hold out in a convenience store or someplace similar for awhile. The movie ends with the boy getting killed by a police sniper's bullet. This movie isn't as old as Laserblast. For the life of me I can't remember the title. Do you remember what it's called?
Sounds like Deadly Weapon (1989). Haven't seen it in a while, and I don't remember it as being very good.
regards,
Apostic