Not sure, but knowing how the RNG works, it would make consume twice as much ammo.
Terraria Community Forums
Kyouko Tsukino
MolochMekkane
With an Endless Musket Pouch you can. Otherwise the closest is something like 75%.
Ringabel
Nope, the percentages don't stack on each other, but on the remaining value. So if you stack 30% on a 50% chance not to consume bullets, you'd have the 30% of that 50%, not 80%.