tex,
Have you tried Trail Boss for shooting small pills in your 88? I load 9,3X72R brass to the top with Trail Boss and top it with 95gr Makarov bullets. They're .365 diameter and 95 grains and make a perfect plinking and small game load.
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.
Where are you finding the B&P short 16ga ammo? They are not shipping any to their new US supplier, so I had them take me off their email list. I REALLY liked their classic 16ga 67mm ammo. I have only one box left, and I strongly don't like the Kent Gamebore ammo. I've found it to be anything but uniform in shot drop and velocity. The crimps tend to fail, also.
