The improved cases will certainly allow higher pressures than a tapered case in most actions, due to the lowered rearward thrust. Excessive pressure for the round is at a higher level - however.

That's a big however, I think. In Ron's guns, the BRNO action seemed to be up to normal or almost normal pressures as he had his ammo loaded, thus they could be improved upon safely, if the barrels, were properly hardened and tempered and stress relieved after rifling in 4140 or 4150 - or whatever is good barrel steel.

If the action used, is not up to the normal 44,000 CUP of the standard case, a straight walled case isn't going to allow higher pressures, if you get my drift.

In the bolt actioned military .303 rifle, it is the action's springiness that limits pressure. In a stronger action, ie: Ruger #1, or other bolt gun like a front lug P-14 or #4 Enfield, the factory ballistics can be improved up, slightly before the case backs up against the bolt or breech face and says "ENOUGH"! Under THESE circumstances, considerable gains can be made using an improved case, ie: lmited taper case.

I agree the neck is shorter than I'd like, as well.

Just where the shotgun action fits in all this, is up to the guy making the rifle and making the CORRECT decisions. I'd think standard SAAMI or CIP specs would work for me in a DR.

Did you know you can sized spent .303 brass, trim to length, slean inside and out, trim off the rim, fill with lead and shoot them in your .457 or .458 rifle?

John Buhmiller used to call them his "mouse hole makers".