Pappy,
Sounds like the same barrel I have. Mine is a GM .54 smoothbore 32" flinter mounted on a GPR stock. Gotta love these guns, even if they drive you a little batty til you find the right load.
If it helps, my load is 70grs FFFg BP, then 2 cereal box cardboard cards punched out with a punch Ohio Ramrod made for me, then 6" of jute twine frayed into a birdsnest, then another card, then 1.5oz (110grs) #6 shot, and another card as OS card. I trust my patterns out to 30yds on most days, and 35yds on a good day, but figure that since Murphy has it out for me, I will limit my shots to 25-30yds if I ever manage to get that close to a turkey.