My best recommendation is to store two integers in your character, or gun/magazine (depending on how your mechanics work) for realism. One for current ammo and one for max ammo. Then when you call your spawn bullet function, subtract 1 from your current ammo (you can set a branch to disable your gun when youre out of ammo as well). Then set up character input to set your ammo to your max ammo variable (you can throw in delays and anims for ambient features)