The question is not how much pressure will double rifles take, but rather how much pressure will YOUR double rifle take? Doubles have beeen built to handle pressures all over the map just as bolt actions have been. There are doubles that take the 458 Winchester or the 375 H&H. There are bolt action rifles that would be converted into hand grenades at those pressures. A given cartridge will run the same pressure in double or bolt rifle.

Cartridges designed specifically for singles or doubles ran rather low pressures for the simple reason there was no need for high pressures. There is no constraint on case length as there is with a bolt action. The 458 Winchester is an outstanding example of a cartridge running high pressure because of length constraints.

Today we have doubles chambered for high pressure cartridges like the 458 Winchester, not because the high pressure is really needed but because of the ready availability of the 458 Winchester cartridge. A 450 3-1/4 would be a better choice in every way except for the fact that you can't buy cartridges at your corner gun shop.

Lower pressures do make for easier extraction, and it has to be admitted the double does not have the extraction power that a good bolt action does when you have a sticky case. But this is not a question of how strong the action is or what it would take to blow it apart.