Most agree that a smooth chamfer or edge break at the muzzle are critical when shooting patched roundballs. There are a number of ways to accomplish.
A lot of folks like to use their thumb and a bit of sandpaper on bore crowns, but I take it a little further, just for the sake of consistency, at least in my opinion.
Here is my method to smooth out or polish a muzzle crown once it has been cut square to the bore that I have posted before. Really minimizes if not completely eliminating patches being damaged at the muzzle when loading.
I use a series of ball bearings, from about one and half times the bore diameter, to right around bore diameter, and use sandpaper of different grits from 120/180 up to 320 or finer (I take it up to 1000 grit for a mirror finish). A couple of turns of the muzzle over each ball bearing with progressively finer sandpaper over them gives a smooth barrel crown to bore transition
Basic idea is to hold the sandpaper over the ball bearing (you can place ball on the floor and hold paper with your feet, maybe on a pad or thin carpet if you don’t have a lathe to chuck up the barrel in) and rotate the barrel bore on the bearing with the sandpaper on it. Easy to keep barrel square with the floor. I’ll start with the larger diameter bearing and roughest grit paper and end with a smaller ball bearing near bore diameter, repeating with progressively finer grit sandpaper. I stop when I have a slight chamfer on bore and rifling lands that is highly polished.
I use Dykem (or a Sharpie) to mark the inside the bore so I can easily see when I starting to clean up everything without going too far. Note the 60° chamfer in the photograph was cut on a lathe, I just use the ball bearings to break sharp edges and polish.
Just note with either method. If your barrel is already finished, you are going to remove finish from the face of the bore if you don’t protect it. I’ve used ‘masking’ tape with a hole punched through it (use a wad punch), but only on other people’s gun’s, not worrying about it on mine.
