My thinking is the effort it takes to uniformly rip the end off a case, in the direction of the shot, would have an equal and opposite effect going the other direction-toward the shooters shoulder. More recoil being the result. The effort expended by the cartridge powder charge to rip the end off may or may not increase velocity, but, I'm guessing not, since more "work", has been done, the work of ripping the case mouth off. Even if it it undesirable work, it costs energy. The expenditure of more energy in this example is more likely to cost velocity, inspite of higher pressure.
My opinion, proven nowhere I know of.
Unless you can think of a reason for this not to be true, I'll run with it, based solely on the one example of a gun that I've seen that does it.
Open to any theories you may have, however.
The gun in question has 65 stamped on the tubes, but, a 16 gauge chamber tool from Brownell's stops a good 1/4" prior to the 2 1/2" mark. Monday morning gun at the proof house, maybe? It is well used, so, someone isn't/wasn't sensitive to recoil. Owner doesn't hunt or shoot it, just a collector. Nothing will be altered on this gun, by him.
Best,
Ted
