This subject of shooting 2 3/4” hulls in 2 1/2” chambers is a recurring question on this board. But perhaps it’s not bad to revisit it every once in a while. As mentioned above pressure tests shooting the longer hulls in short chambered guns did not raise pressures significantly, only 500 to 1,000 psi. That’s normally not a significant amount of pressure. And long ago, when American makers still cut chambers 2 5/8” they recommended using 2 3/4” shells. They wanted to hull to open part way into the forcing cone, believing the longer hull would provide a better gas seal than the shorter. Most of my doubles are damascus barreled with short chambers and I only shoot 2 3/4” in all of them. Never a problem. If my 2 3/4” hull mouths are not frayed after firing I am comfortable that the hull mouth remained in the forcing cone and is safe.
However, one word of extreme caution: regardless of hull length be sure the pressures, velocities, and payloads are within the design limits the gun was made for.
