The 6700 psi crusher rating gets close to 9000 psi on the pizeo pressure measurement system. Yes, the Skeeters will absorb most, if not all, of the breech pressure. And, yes, the expansion of the barrel will reduce the pressure a lot. So, if the gun is in shape for 2 1/2" CIP 12's, it ought to be fine with the 28's in Skeeters.