My theory ( that I'm stealing from someone else) is that the magazines that we put into the gun are just glimmer canisters. Just take a look at the new scout rifles, how does the bullet get to the barrel. Cause it's programable matter. It's transported when a program goes to the clip, telling it to create another bullet and send it to the chamber. With hand cannons, the cartridge that you put into it is a cartridge of glimmer. This can also explain why if you switch from a hand cannon to pulse rifle, you still have ammunition, with the inevitable loss of some glimmer.