it is not "pressure" alone, but pressure per area. The larger diameter case spreads pressure out over larger area and works the action more. .223 at 55K CUP is acceptable. .30/30 at 45K CUP is acceptable. .308 at 55K CUP IS NOT. (or .243.) .45/70 is o.k. with trapdoor loads (under 20K CUP) but not with Ruger 1 and bolt action loads (40KCUP). Mike Bellm has his Triad series on the .444 Marlin Case for use with these lower pressures. And a long, imported .22 European case that gives .22/250 preformance out of a narrower rimmed case so the higher pressure, like the .223, is sufficiently containeddirected to be safe. Even exceeds the .222 Mag Improved... He rants much on his web site. enjoy. luc,