A few years ago a local shop had a 7E serialed in the 500,000 range. It was a 12 bore and was stamped 2 3/4". I checked with Walt and that was the way it was made. I am not sure if the gun had the lug through the receiver bottom. That seems to be one way to recognize a magnum frame. Are there other ways, such as measurements ?

http://www.bakercollectors.com/