When it was introduced, the Model 12 was only available in 20 gauge, 12- and 16-gauge Model 12s became available in late 1913. A 28-gauge Model 12 was brought out in 1934.

The Model 12 was offered in multiple gauges. In fact, the first Model 12s to hit the market were 20-gauge guns although 12- and 16-gauge offerings came out in 1913 and the 28-gauge debuted in 1934.