Did your Gunsmith measure it with a modern chamber gauge built to current SAMMI specs. Many older guns will read "Short Chambered" with these gauges when in fact they are simply a bit undersize in diameter. A chamber only has to be .00125" under gage diameter for it to show Ľ" short. Even if it were not 2 3/4" it would be almost a given that as an American made 12 gauge it would have 2 5/8" chambers, not 2˝".

Miller/TN
I Didn't Say Everything I Said, Yogi Berra