I won't shoot factory American 2 3/4" shells in 20's or 16's with short chambers (either 2 1/2" or 2 9/16"). But I will reload American 2 3/4" 20 or 16ga hulls--most of the 20's with 3/4 oz of shot and the 16's with 7/8 oz. If those loads are pressure tested in the 8-8500 psi range or lower in the 16 and under 9,000 in the 20, I don't worry. And I've never had any that have given any indication via inspection of the hulls that anything dangerous is occurring. Something you can do to offset some of the increase in pressure from the longer hull-shorter chamber combination is to have your forcing cones lengthened.
