Imagine this as far as a Rail/Gauss rifle goes. Instead of buying 30-06 ammo at a dollar a round, I can buy a spam can of 7.62X54R surplus firing a .308 bore shot. No powder, no corrosive salts, no recoil, no gunk, no shell casings. The price of ammo would be much lower. I'd use it.
If any of these worked, you could easily have a magazine tube running on the top like a shotgun where the bullets are held and a magazine containing an energy source so that you could reload either.
I imagine a laser could easily be considered a destructive device. A typical bullet fired by magnetism? Not so sure.