The consensus on the PGCA website seems to be that Parker cut its chambers 1/8 in shorter than the expected shell length, feeling that the overlap into the cone sealed the shot charge better. Thus, 2 5/8 in chambers were for 2 3/4 in shells. That said, I shoot 2 3/4 shells at 1165 in my 2 9/16 inch 16 gauges without incident. If the barrels are sound, and the chambers original, you should be OK.