Brian,
I just read of a 7800 psi 7/8 oz. load recipe in 2 3/4" on the Hodgdon site using Longshot. Alliant has some good prospects in both 3/4 and 7/8 oz. One was 7200 psi with a pie crimp. Assuming Sherman Bell's testing is also applicable to 20 gauge, then there would be no harm in using it in a short chamber. If you still prefer the short shell, then trim 1/4" off the hull and roll crimp. Roll crimping a pie crimp recipe often results in lower pressures by 200-500 psi. Check out online reloading data by all the major powder companies for further possibilities in 2 3/4" for roll crimp conversion to 2.5". Gil
