I just had an idea that is probably very broken but... Teleport gun anyone? As in shoot to teleport to where the bullet hits?
There was another weapon like this, pretty neat concept.
"Trap Gun"
When you shoot once, a bullet spawns but doesn't move. When you shoot again, the bullet flies out in the direction it should've been moving. Does more damage the longer it remained still. (could be easily done by scaling the projectile, which also makes for a neat visual effect)