Model 12's are weird. I have a 1913 20 gauge Model of 1912 with a 25" solid rib, full choke 25" barrel. I also have a mid-1950's plain barrel 20 gauge Model 12 with a 25" full choke barrel, with original-looking serial numbers. Winchester did not make a 25" 20 gauge in the mid-1950's. Barrel appears uncut, still mics at full choke. The 1913 gun is marked Nickel Steel with 2-1/2" chamber, and the 1950's is marked (I think) Win. Proof Steel with 2-3/4" chamber. Go figure.