If indeed it is 58 caliber. 575 ball would require nothing more that a .10 ths size patch. 570 ball would require a patch 15-18-ths and would also require trying each patch with many different Charges for best accuracy. Thompson Center did make at one time a 56 caliber smooth bore Renegade. It was kind of a dual purpose rifle being a shotgun if need be? and a smooth bore rifle too. Using a 56 caliber ball would be to small to use in a 58 caliber barrel I would think? I don't suggest doing so. I've never tried myself. As I do have a 58 caliber T/C Big Bore Renegade myself. And remember the 58 caliber rifled barrel was designed to use a #11 Cap not a musket cap. Musket caps were intended for musket rifles. Some guys changed out their #11 nipples to a muskets nipple in hoping to get a better/hotter ignition. But, doing so it really isn't necessary if your using the correct powder designed for this specific caliber (
2-FF Gorex Black Powder or Pyrodex RS ) would be preferred. Good luck,
P.Script: Don't expect this short barreled weapon to be a long distance game getter. Be happy to hit a 5" target consistently at 40 yards if your able too.
