bigokie,

Another consideration in deciding on a suitable action/cartidge combination is cartridge head size, for a variety of reasons, viz;

1/. Firstly, to allow for sufficient chamber wall thickness, a bigger head size will obviously require an action with a standing breech big enough to accommodate the barrels. May be an issue if you are thinking of using a small bore Ruger U/O action.

2/. The bigger the area of the cartridge base, the thrust on the standing breech is proportionately higher. The reason why doubles for smaller high intensity cartridges can be built on lighter frames. Probably the reason why the pressure "king" of British NE's the 450x31/4" which originally went to 17 ton/sq.in was manageable, by virtue of it's comparatively smaller head size.

3/. Although preferable that you do not use an action with disc set strikers, if you do, the base diameter has to be big enough to ensure that it is adequately supported by the standing breech, and not the striker discs.

As for pressure, here are some CIP pressures taken from the 1989 British Rules of Proof. Presumably, these figures reflect what can be achieved with modern loads.They are given in "bars", and expressed as the Highest Mean Service Pressure (Pmax). The Highest Individual Pressure(Pk) is rated 15% above that and the Minimum Proof Pressure(PE), is 30% over Pmax.

300 H&H.....................3700 bar
450/400 NE 3" ............2500 bar
450/400 Mag.NE 31/4"..2600 bar
450 NE 31/4"..............2700 bar
470 NE..................2400 bar
500/465 NE................2200 bar