Doverman,
Newtons third law of motion applies to this issue it reads; " Every force has an equal and opposite force". To quote Burrard ,In the case of the shotgun the force generated equals;" The sum of the total "ejecta" [the combined weight of the shot charge + weight of the wads + the weight of the gases generated by the combustion of a specific powder.]x the velocity that the "ejecta" leaves the muzzle. Burrard discounts the effect of the drop in "ejecta" velocity during its passage up the barrel as being in theory a valid factor but in practice of no real significance.
As stated by others; the lower the velocity for any given charge[ejecta] results in less stress on the action components of any gun and of course the resultant recoil to be absorbed by the shooter.
