Re: Glock 19
Recoil is a momentum based calculation at the start, you launch a bullet mass and powder mass out the barrel at a given velocity, the gun has a mass of its own and recoils backwards at a velocity proportional to the velocity of the ejecta (bullet and powder). In other words, there is an exact equivalence between mass times velocity in each direction. Note that velocity is not squared at this point. Then, you take the velocity of gun going backwards and apply that kinetic energy formula listed above.
So, in general, for a given case, pressure, etc., if dropping down in bullet weight lets you increase velocity by a greater percentage than the loss of bullet mass, your recoil will go up, or, vice versa.
Oh, I love my G19's. the Black Hills 124 +P gold dot at better than 1250fps rocks.