That IPSC shooter had it about right. The reason is that a significant portion of the recoil equation is based on the kinetic energy of the projectile and the propellant gasses. As you no doubt know, kinetic energy is calculated by taking half the product of the mass involved and the square of the velocity, so that as velocity increases as it must to maintain a constant power factor (which is closely analogous to momentum and is the product of velocity and weight) the effect is to increase kinetic energy even though momentum is constant. The increased energy is felt in recoil. Different powders will contribute to give different recoil signatures as well and can affect a shooter's ability to stay on target or make a smooth transition between targets.

Cheers,

Norm