The old British Game Load for the nominal 2 1/2" chamber of 3 tons per Sq inch translates to right at 9,000 PSI as recorded by modern Piezo Electric crystals. This is "Max Chamber" pressure.
One thing to keep in mind is recoil is "NOT" directly related to max chamber pressure. It is related to the max weight which is ejected from the barrel (shot, wads & powder) & the velocity at which they are ejected.
Max chamber pressure applies to how much the camber walls are capable of withstanding. Personally if the chamber walls are "Too Thin" or in too bad a condition of holding 8,000 PSI, that gun is simply a "Wall Hanger".
Stock troubles are related to recoil, not chamber pressure. Recoil as stated is related to oad IE matter ejected & speed of ejection. If you want to protect old wood use a lighter shot load &/or a lower velocity. Hope this helps but do feel free to ask further questions you may have.
