Originally Posted by Researcher
Only the very latest Model 310s, 1947 and later, were chambered for 2 3/4-inch (70 mm) shells. The exception was the Model 310X the Pigeon Gun which was chambered for 70 mm shells.


I read that as well so not sure if it was changed at a later date to 2 3/4 or not. It was sold to me as 2 3/4 and my measurements verify this. I was curious if any were made 70mm and if so would they be marked.