I generally won't build with any cartridge over 40K psi - less is better. Most of the large British cartridges: .450's, .465, .470, .500; are in the 34K-36K psi range. As I have pointed out in other posts, one of the limiting factors in using a shotgun action, is that the fit at the "circle" is generally not as tight as with a double rifle. See Vic Venters book "Gun Craft" and the chapter on this subject. There is a way to solve this "loose fit" at the circle (shown in Venters' book), but I have not done one yet, so hesitate to pontificate too much this subject at this junture.

"Not knowing to any degree of certainty and, not wishing to propagate an error, I hesitate to respond."

My recommendation is to keep things under 40K - less is better.

Ellis