MD, Remington made 2 commonly produced sizes. Easy measurement to check is the distance between the centers of the firing pin holes. 1" for Small frame. As I understand it is that both 12 and 16 were made on both size frames. 12's could be had on small frames, 16's on large. Soon, the knowledgeable Remington guys will jump in and have a the particulars on the Rems. Randy


RMC