Miller, we do know from Bell's tests that pressure does increase when firing long shells in short chambers, although usually not a significant amount (a few hundred psi). And we also know that lengthening the cone usually results in a reduction in pressure, vs a short cone (from the same tests). Of course that doesn't tell us anything about recoil, because those tests were conducted in a pressure gun. The 2 3/4" low pressure reloads I've fired in short chambers--many thousands of them--generally seemed quite mild in the recoil department. But then I never compared them to the same load fired in a hull cut down to 2 1/2" either.