chain fire would be no worry, what happens there would be the ball firing with the chamber not in station so going along the outside of the frame rather than the barrel, you are not using balls.
Keeping the powder in you would use a wad, perhaps tissue pressed on top the powder maybe with a light brushing of grease to make it stick better.
“If a cricketer, for instance, suddenly decided to go into a school and batter a lot of people to death with a cricket bat, which he could do very easily, I mean, are you going to ban cricket bats?” :- Prince Philip said after Dunblane