Folks, I swear this is something I never thought about when I was shooting smoothbores in Northwest Trade Gun Matches, but it is something someone came up with on the U.S. International Muzzleloading Team and I learned about in the mid 90's.
At a tryout match in 1996 to pick the team the for the World Championships, someone came up to me and asked if I had any sandpaper with me. I usually kept 220, 320 and 400 grit emory cloth, but they wanted 80 grit. I asked the shooter what he wanted it for and he said "to sand his balls." Well, needless to say I thought I was being set up for being the butt of a joke, but it turns out they did that on the smoothbore musket matches. 1816 type muskets were the preferred gun for the original musket matches. One of our best shooters used an original M1840 musket, so I asked him about it and he said, "Yep, that's true." No one had a scientific explanation for it, but they thought it gripped the patching material better and it did make the muskets more accurate.
So, when I packed my gear for the World Championships, I added five sheets of 80 grit emory cloth and danged if they didn't use every one of them to sand balls for smoothbore muskets. They won a Gold Medal in a combined firearms match due to how well our musket folks shot, so it did actually work.