Ball cutter mounted in a drill press, scrap wood guide and stop clamped to the bed of the drill press.
Jig built to hold the cylinder and while you advance along the guide until stopped.Pop the cylinder off, rotate to present another well for cutting. Use cutting oil, go somewhat slow. You adjust your length of travel so that the ball completes its cut but never touches the inner wall of the nipple well.
Wadd, caps do not fall in mainly because there is not the gap in the rear of the frame where the hammer goes, such as on a Colt clone. The other half of the equation is changing out to Treso nipples or similar, which hold the caps for a snug fit through the detonation process.
RCJ