Ditto the last comment. A drill guide is important or the drill will walk right into the rifling. If you can't find plastic tubing that fits the drill, go to the hobby shop and find a piece of the K&E metals telescoping brass tubing and pick a size that does. You can wrap the outside of it with masking tape until it just drags going down the bore.
If you've watered the powder already, I would additionally squirt it full of Kroil or PB Blaster or other penetrating oil. Ditto on the ball. After the hole is in the ball, squirt some down the hole just to be sure.
You can also tap the hole for a 3/8" bolt, if need be. Same as guntotin_fool advised, you just need to use a washer and a bolt long enough to screw through the threads. Then just turn the ball out.
If the ball strips out and is still stuck, see if you can flush the powder out through the hole by running water into the nipple? Once it is clear and rinsed out, find someone with an Outer's Foul Out. It would be slow going to remove all that lead electrolytically, but it could be done. This assumes a patch isn't insulating it from the barrel steel and that the bore has no rust (which will cause a Foul Out to start removing steel). The reason for getting the powder out first is to prevent the Foul Out lead solution chemistry from changing during the process.
Nick