[mrerick]

Recoil force and feel goes back to Isaac Newton's principles - every force is met by an equal and opposite reaction force.

The forward acceleration of the bullet mass and the exiting gunpowder gasses creates the recoil force felt in the firearm.

The faster the bullet mass is accelerated, the more force involved. On the artillery Luger, the bullet spends 2 1/2 times as much time being accelerated by the powder gasses before it exits the barrel at maximum muzzle velocity, and then starts slowing down as it travels through air.

For the entire time the bullet travels down the barrel (a time longer than the regular Luger) the acceleration continues resulting in greater speed. This transfers greater energy into the bullet by the time it leaves the barrel, but also spreads the buildup of energy over a longer period of time.

The bullet leaves the artillery barrel at a faster muzzle velocity. The felt recoil impulse is longer than in the 4 inch barrel Luger.

Classic Newtonian physics account for the recoil you feel in both pistols.