I agree, Dave, and I don't have the instruments to do so. Hopefully, someone around here will, but I live in a rural area and bore gauges are few and far between! Thanks!

[QUOTE=Robin Lewis;132674]Here is a video in which Larry shows how to measure a 11 gauge chamber so he can make custom brass shells to shoot. It would be a good guide to find out what gauge you have. He measures the chamber at about 3:40 into the video. I hope this help.

Very interesting video, Robin. Yes, this helps tremendously! I'm just wondering if a cast of the chamber is necessary rather than a direct measurement, although I suppose that would be rather difficult and prone to error. With the cast, you can take a direct measurement and be assured your results are accurate and repeatable.

Jack, I think your first step would be to try to load a new unfired 12ga shell in the chamber. If it fits easily, then problem solved. If it's very tight, then further accurate measuring is required.

By it's age, the gun was made for use with brass shells and if you intend to use a 12 ga. shell to determine if it is a 12 ga. gun you should try a 12 ga. brass shell.

I'm not a shell person but I seem to remember that there were two 12 gauge brass shells. I don't remember the designations used? Maybe someone could "remind" me and inform others?

Thanks, Dave. I have tried both a 12 and a 16 ga. shell in the gun. A 12 gauge will not fit into the chamber (shell is too large), and a 16 gauge (to the best of my recollection--it's been a while!) falls right through the barrel.
Do you think it would be possible to find a dowel or piece of plastic pipe that fit snugly into the chamber (without getting stuck!) and then measure that instead of making a casting---I'm a little nervous about attempting the casting process!

Thanks, Dave. I have tried both a 12 and a 16 ga. shell in the gun. A 12 gauge will not fit into the chamber (shell is too large), and a 16 gauge (to the best of my recollection--it's been a while!) falls right through the barrel.
Do you think it would be possible to find a dowel or piece of plastic pipe that fit snugly into the chamber (without getting stuck!) and then measure that instead of making a casting---I'm a little nervous about attempting the casting process!

P.S.By very tight, you mean that a 12 ga. will actually fit into the chamber, except very tightly? One will not even start into the chamber on this gun. Maybe it is a 14 ga. after all! BTW, a penny is almost the same size as the chamber at the end of the barrel..only the penny is a few hundredths too big. If placed in the chamber, about half of the penny will rest inside and the other half will protrude. The Redbook lists the diameter of a penny as 19 mm.

A brand new 2013 penny measures exactly .751" in four different locations across its diameter.

Cast with candle wax. It will be soft so working with it may be difficult to get an accurate measurement?

Thanks Dean--excellent point! I just dug out an old Winchester brass 12 gauge and tried it. It's close, but it will NOT go into the chamber at all.