I was looking thru my 1992 Thompson Center Owners Handbook and saw that they dedicated page 39 to page 50 to their T/C Muzzleloading Shotgun. They say it is a 12 guage and it came in two different models. One with a screw in choke tube and one without a screw in choke. This model that doesn't have a screw in choke tube is a cylinder bore. Looking at the photo that they show it appears to be a half stock, round barrel shotgun with a single trigger. The "12 GUAGE TRAINING & CLAY TARGET LOAD" they show is for 70 grains of 2Fg black powder with, "Either 2 T/C 12 guage, 1/2" Fiber Cushion Wads. One wad over the powder and another over the shot as illustrated on page 41. Or, Two 12 guage Natural Wads Over The Powder And One Over The Shot." This load is for, "approx. 1 oz. of shot." They also list a, "12 GUAGE HUNTING & CLAY TARGET LOAD" with 80 grains of 2Fg black powder with, Either Two T/C 12 guage 1/2" Fiber Cushion Wads. One wad over the powder and another oer the shot as illustraged on page 41. Or, Two 12 Guage Natural Wads Over The Powder And One Over The Shot." (The capitalizations shown are theirs, not mine.) This load is for 1 1/8 ounces of shot. I guess the reason I'm posting this is, I have never seen a factory made T/C single barrel 12 guage shotgun. Have you?