Sherman Bell's "Finding Out For Myself" Part V was a study of shooting longer shells in a short chamber and he did find an increase, note as "insignificant" 10% or less but an increase. I would suspect difference in forcing cone length and bore diameter would also be a factor. I have 12ga shotguns with bores that run from .710 to .732 and forcing cones that go from almost shoulders to fairly long tapers
I think the statement "2 3/4" with the appropriate pressure" is the big issue here. The factory 2 1/2" loads I shoot (B&P High Pheasant) run in the 6000psi 1 oz and 7000 for the 1 1/16. Finding modern 2 3/4" ammo with that low of pressure would be quite a problem as most 2 3/4" ammo is a quite a bit higher pressure to run modern gas operated Semi-auto's reliably.
I still think that if the gun has 2 1/2" chambers, that's what should be shot in them.
Last edited by erich; 05/10/18.
