Just curious, but who made and what is the pressure of your shells that make them safe for old guns ? I have three Damascus Parkers, one Damascus Lefever, and six Damascus Remingtons along with three steel barrel Remingtons, all built in the 1800s. I shoot all of them, one or the other, three times a week with nitro powders. All 2 3/4" shells even though all of them are chambered for 2 9/16, 2 5/8, and some 2 3/4. My mild pressure shells [ under 8000psi ] will only go up about 500psi in the short chambers. At least one gentleman tested 2 3/4" shells in a 2 1/2" chambered gun and that's all his shells went up. I'm not telling anyone what to do, just what has been done. Do what you feel is safe.
H&A made some of the finest SxSs back in the day. They apparently had the copy rights to some of the best English doubles. My how times have changed. Today they're just a cheap gun. They didn't make them for long but now a days are considered the best of the best. I wouldn't worry about the quality of the barrel steel.