The Model 12 actually came in 12A, 12B, 12C models. The Model 12A had a round barrel, while B & C had octagonal barrels. The Model 12B was a short barrel rifle.
This firearm was introduced in 1909 and the last one, a model 12C was produced in 1929.
Actually, Remington made the Model 12 until 1936 after which it was replaced by the Model 121.