JDW, many of us use light shot charges (24 gram, 7/8 oz and 1 oz) and low pressure loads in 2 3/4" hulls without ill effect. However, we all recommend that if you see damaged hull ends, don't continue to shoot 2 3/4" hulls. Generally, 2 3/4" hulls are ok in all but guns with very short forcing cones. From the dimensions given, I suspect your barrels may have been pitted near the breach and honed more there than near the muzzles.