Really dumb stuff for the gunsmith:
It's never explicitly mentioned just what *your* gun requires to keep working. But the arcane magazine weighs nothing and happily holds all the tools required while still weighing nothing. So try and sneak a few extra things in there, like an anvil, a mini-forge, a sledgehammer, a crowbar, a grappling hook, some thieves tools, 400' of rope, etc. It's a *very* complicated weapon, and it *needs* all these tools to keep functioning properly. You're just using them for other stuff in the meantime. They all fit in the pouch too.
Speaking of weight, bullets weigh nothing. They might be made of lead, but it's "magic" lead. This means they have an incredibly low density. So they float. In fact, they don't only float on water, they float in the air too. The gun and the ammo pouch float too, so be sure to tie them to a rock or something if you have to lay them aside. Bonus points if you manage to construct an entire airship from lead bullets (it may take a while).