Miller, I realize that Thomas was a gun writer; therefore, in your opinion, of low credibility--unless he happens to agree with you, which would make him one smart guy.
However, he was also an engineer, and I think on this subject, his credentials are at least as good as yours--whatever yours may be.
What Thomas does not state, at least not with total clarity, is whether the shells loaded with the faster burning powder had a lighter powder charge than the ones with slower burning powder. That, of course, would explain why they recoil less. He does specify that the shot charge and velocity were the same, and since he was an engineer--although I don't like to assume--I think it's likely a safe assumption that he realized that a lighter powder charge of faster burning powder, producing the same velocity as a heavier powder charge of slower burning powder, would automatically mean reduced recoil. That puts us back at his conclusion that ALL THINGS BEING EQUAL--same weight of ejecta, including powder, and same velocity--the faster burning powder will reduce recoil.
I don't know if he's right or not. Perhaps time to turn that one over to Mr. Bell as far as measurable recoil goes. Felt recoil . . . well, some people are skeptics when it comes to anything that can't be measured. Except, perhaps, the existence of God.
To return to the original question, I'd say it's highly unlikely that 2 3/4" shells, reloaded to 7,000 psi, would be dangerous in a Lefever chambered at 2 1/2". Pressure might increase slightly, per Bell's experiments. Recoil might also increase if the gun has especially short and sharply tapered forcing cones--in which case one might not want to use the longer shells in that PARTICULAR shorter chambered gun. Or else lengthen the cones.
