I got Hornady Balls...

It was the diameter. The pistol ones would not work in the rifle if I remember correctly ( 20 plus years ago). I believe the pistol balls were way too small. Track of the WOLF list 19 different sizes of 30 cal. balls. .350-.389. You can always make up some of the gap with thicker patches or multiple patches. But these were way off. The container was labeled "Pistol balls" and whoever I ordered them from made it right. This was before the internet mind you, and if you weren't in the loop on muzzle loader things, it was all trial and error. All calibers have a list of sizes that varies. If you hear someone say their muzzleloader is too hard to load, they simply need to mic the inside of their barrel, subtract the thickness of their patch and then pick the correct size ball or projectile. Muzzle loader barrels differ greatly on size within the same caliber. Knight rifles use to be the most consistent of the mass production rifles. And the older CVA with the Spanish barrels were probably the worst. Part of the fun of shooting a older model muzzle loader is "working up a load" as they used to say.

Pistol ball should be larger. They are intended to be used without patch.

My sons 44 caliber 1858 New Army wants .454 ball my 45 caliber Ruger Old Army wants .457. While a 45 caliber Hawkin Pistol wants .440 ball and the 50 wants .490 ball.