First, recoil is based on the simple formula that the mass times the speed of the "stuff" (bullet, powder gas, unburned powder) going in one direction equals the mass times the speed of the "stuff" (gun, scope, sling) going the other way. This is Newton's "equal and opposite" law.
But the main component of the forward moving "stuff" is the bullet. It moves fast and goes far. The main component of the backward moving "stuff" is the gun. But the gun is heavier, so its speed is less and it doesn't go as far or as fast.
Recoil begins when the bullet begins to move. If the bullet doesn't move (if the barrel is blocked), there is no recoil. (Hatcher's experiments confirmed this and, incidentally, the M1903 rifle he used did NOT blow up.) Further, if the bullet cannot move and there is no recoil, a recoil operated pistol, like the M1911, will not operate. My own experiments have confirmed that.
So, with any given weight of bullet, powder, etc., and any given weight of gun, the recoil will be the same IF THE GUN IS FREE TO MOVE. But the gun is not free to move when being held by the shooter, so his body enters the equation and becomes part of the rearward moving mass, further slowing and restricting the movement of the gun.
OK, so what about "perceived recoil"? What about what we feel when we touch off a .44 Magnum? That is where such things as stock/grip design, stock and grip material, and similar items come in. If the buttstock of a rifle came to a sharp point, so the momentum was concentrated in a pinpoint, that rifle would be quite uncomfortable to shoot (to put it mildly). But if the stock is wide so the momentum is well distributed, firing the rifle will be pain free. A recoil pad, which spreads the momentum over time as the pad compresses, also reduces felt recoil.
Given a certain bullet mass and velocity, and a certain gun mass, there is nothing we can do to reduce free recoil. But there is a lot we can do to reduce felt recoil.
Jim
