L C Smith chamber drawings for 1907 show the 12 gauge had been standardized at 2 3/4". It was possible I believe to order chambers cut to a non- standard length, so always wise to measure. Drawings for 1922 show the same.
Most of the odd lengths were done away with by around WWI, so this one is highly likely to have a 2 3/4" chamber.


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