Bill,
Your post about accepting burned powder as "ejecta" (as related to Uncle Issac's law: for every action there's an equal and opposite reaction) brings to mind the solid boosters on the Space Shuttle (or a jet engine burning kerosene). A bit of rubber with some mag and alum in it, burning makes some heat and pressure and has only one exit path thru nozzle at high velocity. It pushes pretty hard in the opposite direction.

I have no argument that the total weight of the "ejecta" and the velocity will get you to a total energy of opposite force (I think the word "recoil" is ambiguous in this discussion). What it won't do is give you peak force in the opposite direction. That requires knowing the peak force against the base of the projectile, which in turn requires knowing the area of the base of the projectile and the peak pressure.

What someone can feel can be debated until the world runs out of beer.