Inline or Traditional rifle? is good to know first. As they (both) require different types of projectiles because of their barrel twist rates. As far as a 54 cal ball? .530 dia. would work good for your application with a 10-15ths patch. I personally shoot .535 dia. with a 10ths. patch out of my 54s. Like I said. Just my personal preference is all. Again just
my humble opinion.