I hesitate to enter into a discussion where physics and engineers tread, but, here I go anyway.

Newton's third law of motion: For every action, there is an equal and opposite reaction.

Years ago I had some contact with the 4.2" mortar and the 106mm recoiless rifle. The 106s were mounted on jeeps. When fired, the projectile left is such a hurry, a vacume was created, sometimes popping headlights and watch crystals. You could watch dust jump off the ground. Yet, the jeep barely moved. Why, as much energy went out the back of the rifle as out the front. The "four deuce", however, has a projectile you can follow with the naked eye for quite a while. I can also remember digging the base plate out of soft ground or firing a couple of rounds to "set" it in the rocky soil of Ft. Hood. That in my book is called recoil.

My point of all this is, the energy of a given projectile, depending on weight and velocity, is going to send exactly the same amount of energy the opposite direction, what I call recoil.

To me, increased pressure can only speed up the projectile, creating more energy, and the same amount of increase in recoil. I think we all pretty much agree, felt recoil can be mitigated by the weight of the gun, recoil pads, and anything else bleeding off the rearward thrust of energy. But, Newton's third law is still there.

As to Joe Wood's Parker tag, I believe all 2 3/4" shells of the period and later were paper and roll crimped. When opened they were 2 5/8".