I think Eightbore is technically correct that there were no 2-1/2" Model 12's. On the other hand Larry is also correct that the "Model of 1912" was originally introduced as a 2-1/2" 20 gauge. Since the Model 12's and Models of 1912 are essentially the same gun, I call this one a draw.
For what it's worth, my circa 1913 Model of 1912, 20 gauge, with original 2-1/2" chamber and ejection port spent most of its life, prior to coming into my hands, digesting roll-crimped 2-3/4" shells with no reported problems. I even got a supply of the old ammo with the gun.
