GH, That's kinda funny in one way, and kinda sad in another.
I've never seen it tried but I can certainly imagine what might happen.
Here's a short story...........
I had a guy shooting one of my old flinters one time from the Bench, this was his first time behind a flinter and everything was going fine, he had instant ignition and was continually complimenting me on such a fine rifle, how accurate, and yada, yada, yada...load & shoot, load & shoot, and so on when I noticed his left hand come around under the rest to set on top of his right hand which was his trigger finger.....
I yelled no, no, no, and reached over to move his left hand from outside the touch hole when he touched one off!
The blow-back from the touch hole took his fourth finger nail off, not really off, but it actually raised it up from its bed and blood was flying everwhere! I thought he was going to faint from the pain, and I just knew he was going to shoot me as soon as he colud get his breath, because I suspect, actually I've always suspected, that he thought I had something to do with that because I started to reach over him.
I must have bought him a hundred beers after that, trying to convince him that what he did he did himself by putting his finger too close to that touch hole.
But, like I said, I honestly think that to this day he still believes it was me, and he has never shot another flinter......as far as I know.
Some lessons come really hard!
Uncle Russ...