2-p makes some very good points on chamber pressure of a "solidly obstructed" breach. The other side is the 12-20 barrel burst scenario. Usually, the burst is at/near the point of obstruction, not at the breach. I think this can be calculated with the right data. I"ll look into it for the future.

"Total Recoil" is the kinetic energy or the gun on firing. It is easy to calculate if the factors are known, and they are easy enough to measure. It is the only thing I know of that correlates to what the shooter will feel when he fires the gun. It is not a 100% correlation; the difference is the subjective "felt recoil." I agree with Chuck that "felt recoil" is knowable, it is just that nobody has done the work.

Pressure contributes to recoil only as it generates velocity of the payload and powder gas. Pressure does not push back on the gun to cause recoil. Recoil is caused by conservation of momentum between the ejecta weignt and velocity and the gun weight and velocity. Recoil pads and recoiling parts within the gun don't change total recoil, but they do change the time span over which it is applied. This leads me to suspect that "felt recoil" is associated with force and/or acceleration of the gun.

Shot does not "slam into" the forcing cone or choke cone. It is at least semi-fluid and flows through these two constriction. The shot accelerates as it passes through constriction and the internal pressure drops (venturi principle). This is an orderly happening, which is why choke constriction works to reduce dispersiion.