Fun stuff. Gee, I have no idea how many ball boards I have made over the years. I have never cared to use them, but I made them.
Petah, that is the way I made mine, with a cut out around the hole. Originally I figured on that countersink as a location area to put the patch, then push the ball through. I started out using a Forstner bit, but found that difficult to center, so I got a 1 1/4" countersink bit with a hole in the middle to put a 1/2" shank bit into, and presto changeo, one easy operation. I probably still have it laying around somewhere.
The few times I have used a ball board, I usually located them on the barrel of the rifle by having the patched ball protrude a bit and located off of that.
Anyway, good stuff here. As always, this is a good place to learn. Bravo !!!
John (Bigsmoke)