Hi George,
Im far away to check myself so, answer some questions please:

Balls are pure lead?
When you put the ball on the muzzle how much of it stick out?

You can try with some thin cloth, start the ball with a big piece of cloth so you can retrive it. Remember that the barrel is coseat the breach.
Also you can make a hole in a ball and put a secrew to retrive it.

Hope this helps.
Martin

PS: I have been waiting to read about your shooting with the .72.