Crimp can improve burn regularity (good for velocity consistency) at the risk of distorting the bullet (bad for balance, though not usually enough to matter at handgun precision levels). Crimping delays the neck lifting away from the bullet, so the powder burn is a little further underway. It has an effect that would be measured in microseconds on the bullet release.
The recoil difference is due partly to powder mass and partly to how high the muzzle pressure is that is accelerating the mass of those gasses to blow them out past the exiting bullet. That gas expulsion is called "rocket effect" and "after effect." In some overbore high-power rifles shooting large charges of slow powder behind light bullets, the rocket effect can account for upwards of 60% of the recoil. Muzzle brakes that just vent gas in all directions rather than favoring pushing the muzzle down, like Magna-porting, or pulling forward on it, like a clamshell brake, are able to reduce recoil because they drop the muzzle pressure just before the bullet clears the muzzle so there is little rocket effect left to push the gun to the rear.
In the case of a handgun, the same principles apply, and the more gas mass there is and the higher the muzzle pressure is, the more rocket effect you get adding to bullet recoil. Broadly speaking, when loads of fast and slow powder have a velocity match with the same bullet, the fast powder will get there with higher peak pressure, lower muzzle pressure, and lower gas volume. The slow powder has to make more gas to achieve the higher muzzle pressure, and that is why, for powders with matching energy content per grain, the slower powder load is heavier, providing more mass to expel and doing it at a higher pressure, creating more reaction force.
