What I've learned, as a writer, is that you always take the extra step to make sure your readers understand. I've been fortunate enough to have some very good editors who've pounded that into my head. We have people here who understand that pressure does not relate directly to recoil--at least not to "measureable" recoil. (What people "feel" is . . . well, what people feel. And difficult to quantify, objectively.) We also have people here whose level of understanding hasn't reached that point. So, when a thread on recoil wanders off into the pressure swamp--without clearly stating that the "pressure" part of the discussion has to do with whether the shells are appropriate for vintage shotguns--I feel it's very appropriate to make sure no one gets lost in said swamp.
As for pressure curves, the ones I've seen--produced relatively recently by Sherman Bell, and produced back before WWII by Dupont--don't show a whole lot of difference, even between smokeless and black. Pressure ALWAYS peaks inside the chamber, and it always declines very rapidly. So whether any difference the shooter feels is due to a different pressure curve, or whether it's due to a difference of several grains of powder, from faster to slower-burning . . . I don't know. The late British shotgun guru Gough Thomas, in one of his articles, expounded on a theory attempting to explain the "push vs hit" difference in the way two different loads feel. He also reports on a blind test conducted in England, in which the shooters of two otherwise identical loads (shot charge and velocity) unanimously chose the one with faster-burning powder as having less recoil. Waters in this part of the swamp remain muddy.
As for American factory shells at 13,900 psi . . . probably worth pointing out that that would be about 2,400 psi above the SAAMI service pressure standard.
