Without definitive information, I took my caliper to Home Depot. There were a lot of the sizes I had at home that would not do with cutting...
I bought a pack of 2 mops... I mean paint rollers... Home Depot brand 3" for smooth to semi smooth surfaces takes a 1/4" center pin... with an OD about right for my 3/4 bore Crown Point Breech loader's chambers.
I bought 2 Wagner 3" Smart Roller Cover(s) with a 1" center hole and OD about right for the golf ball bore cannon. With the smaller center hole, it has thicker nap so more give to fit the bore.
additional
The 3/4" is a tight fit in the interchangeable chambers. I had to work to pull the end plugs out. I might look for a shotgun mop instead.
The larger size is a nice fit in the GB bore... a bit loose on the 1" dowel but it'll work. Again, a bit of work to removed the end fittings. I ended up cutting the open end lengthwise with a loose hacksaw blade so I could pop the glue. The closed end I was able to drive it in with a dowel & then back out to free it.