fla3006, I believe SAMMI maximum pressure for a 12 gauge is about 11,500 psi. That is way above what the service pressure most short chambered guns were designed for. And just about all American ammo is loaded towards that max. Not because it gives superior performance, it doesn't, but because high chamber pressures are needed to operate most automatics. Virtually identical downrange performance can easily be accomplished with 7,000 psi or thereabouts. That's well within the normal 3 tonne proof most British guns have.

John McCain is my war hero.