rennikselum - I think any similar burr would work. I use a lot of various size and shape burrs for dental and jewelry work. These are just some of the round ones. The larger ones are the burrs I would use with this tool.
SBachner - The dovetail slot in the round bar holds the cross bar. I put two slots in the round guide bar so that I can get the cutting tool closer to the end for the molding at the rear pipe and at the muzzle cap. I can move the tool holding cross bar to either position.
By the way, if you intend to make one of these, make the round guide bar at least 6 inches long. I made this one 3 inches and it is really too short as it does not glide over the ram rod pipe inlets without a wobble. It works fine, but you need to be careful around the pipe inlets. A longer guide bar would just make the tool that much easier to use. I will update this one and show it when I get it done. And also, I made the first version of this out of wood. I cut a 6 inch piece of 3/8" hickory ram rod, filed the dovetail slot in it, and made a hardwood dovetail cross bar out of scrap maple. I drilled and tapped the 6-32 holes for the clamp screws right into the maple. If you didn't want to make one out of metal (brass or aluminum or steel), it would be better to do this out of hard plastic. The threaded holes for the clamp screws would last much longer than they will in maple.