Pressure does not enter into the formula for calculating recoil at all, only motion & wt.
I agree with all of your statements concerning recoil and pressure and their effects on the gun, Miller. And, as far as "calculating recoil" goes, with the above statement, too. Calculations, however accurate, do not totally agree with what I perceive the recoil to feel like. And, to take it one step further, and to parlay it into a partial answer to David's question as to how it affects his gun, I think burn rate of powder and the resulting "sharper" pressure spikes resulting from faster burning powders' use (read promotional loads here), also deliver a "sharper" blow to my shoulder, but more importantly to the head of the wood stocked gun. Even though the calculated ft.lbs. of recoil may read the same on paper.
A black powder load pushing 1 1/4 oz. of lead at 1100 fps will not feel nearly as "punchy" to me as a very fast burning smokeless load of the same weight and velocity out of the self same gun. I know you must have felt that difference as well. I believe that "sharpness" of recoil, i.e., the same calculated recoil delivered in a shorter time span will deliver more punishment to the wood at the stock head. Agree?
Truth be known though, that difference may be lost on a well inletted stock head and a piece of very dense and dry wood. If not lost totally, the differences in damage to the wood may, or may not, be incalculable.
