Welcome to ZDF!

I was still having the bullet decal issue, but I solved it now. Edited the OP with the solution.

Yeah, I just realized I was woefully misusing that inventory class. I adapted that from a similar example, but I think that was removing and not adding a weapon. The ammo immediately maxing out should have tipped me off. Thanks for the help!

EDIT: After using the solution in the replies, I was still having the decal issue. I've solved it now, so here's the fix for future Googlers: Create a file in the root of your mod called "decaldef.txt". In there you can add a definition that looks like this: generator TestWeapon BulletChip Replace ...