Bruce; what a wonderful Nickle Steel Model 12! I've seen a lot of those early model 12s but never one as nice as yours. I own one
like new model 12 and it is a 1962 gun, made the year before they stopped regular production.
Have you checked the chamber length on your gun? I read that some of the very early guns were made for the 2 9/16 shell. (I think that's the length.) I had my 1923 gun looked at and the smith said it was short and he lengthened the chamber.
My gun and she is not exactly pristine!
Threaded Mode