Some were chambered for 2 1/2" or 2 9/16" shells, especially the early ones. That has never stopped people from shooting standard 2 3/4" shells through them, but it might be something that needs to be checked. I believe the one I have is a 1931 model and it is 2 3/4", it also has the slightest of a ring or bulge about an inch in front of the barrel attachment point just in front of the forearm. It is so slight that I almost missed it when I looked the gun over initially. Since then I have shot over 4000 rounds through the gun and no additional problems.