If the crown has sharp corners you will have difficulty loading combinations that are easy to load, with a nice smoothly radiused or rounded crown.
We've loaded .508" balls in a barrel with the same dimensions as a Getz .50 barrel, using a .019" ticking patch, without damage to the patch and without difficulty.
Normal trail walk or hunting loading is a .495" ball of pure lead, and a .0205 to .0225 denim patch - mink oil, spit, neetsfoot oil, or WWWFluid with a tich of oil added. All work equally well. If anything, the mink oil from track loads the slickest, but it's difficult to beat spit for accuracy and ease of loading for target shooting.