ss1: IMO, muzzleloading single shot pistols should be held in the hand while loading, not resting on a table or bench.
If one rests the butt of the grip on a bench, they stand a good chance of cracking it when the start the ball/patch.
I have used a plastic headed mallet that I got at the local hardware store on the Cheap Tools table, or a short starter to start the patched ball.
Using the short starter is kind of a challenge but my method is as follows:
Using my left hand, I hold the forward end of the barrel pointing up and using my lower three fingers to force the barrel into my palm.
Then with the index finger and thumb holding the short starter ball, I give it a whack with my right hand to start the ball/patch.
To help with this loading, I use real thin patches with a normal ball. For instance, in the case of a .50 caliber, I use a .490 dia ball and .010 thick patches.
It's kind of a pain in the rear, but it beats cracking the pistols stock.
zonie