Just what kind of shotgun are you shooting? A quarter is 0.955" in diameter, a 12gage bore measures 0.729", a 10ga is 0.775", an 8ga is .835", and a 4ga is 1.052". A dime at 0.705" and might fit a 12ga and a penny at 0.750 might fit a 10ga but they be could be tight in the shell casings. That doesn't allow for a choke either.
I saw a 4ga once. It was about 8 feet long and had a swivel like an oarlock about halfway down the barrel. The owner called it a "punt gun" and said it was used for duck hunting from a small rowboat (a "punt"). I gathered the idea was to find a raft of ducks sitting on the water and sneak up on them through the weeds, then let loose with your single (black powder) shot and gather up the dead ducks. Don't know when it was last used as hunting with anything larger than 10ga. is now illegal.
Regards,
GtG