[sewerman]

usually the .575 is correct for the Italian guns.
i have an armisport 1861, springfld & 1853 enfield and they both use the .575.
historically the enfield was calibred in .577...but the .575 works and i have found it very POA , POI. i know several mold companies produce different sized minies ...lee offers the largest size selection,but usually the .58 cal fall into the .575-.578 sizing. the R.E.A.L. bullet comes in .592 but this is not a traditional minie.

you may have a deformed bullet as you mentioned. though i have never experienced a minie just dropping down the barrel. they fit loose and the hollow base is expanded by the gas & pressure, forced into the lands and grooves of the barrel as the bullet is pushed down the barrel.

when these rifled muskets were front line weapons there were clean out bullets type I-III which looked like a minie but used a zinic disc at the base which flattened out as the gases pushed the zinic base into the bullet on it's way down the barrel to clean out powder residue. they were packed every fifth bullet in the cartridge boxes. most soldiers in ignorance just through them out ...?

so you will have to brush your bore every 3rd or 4th shot if range shooting for any length of time.
also the ffg powder works better than the prefered fffg. the larger granules allows more oxgyen to be trapped when loaded which helps for a better burn contrare to popular belief.

enjoy your musket!

S.M.