crbutler wrote:A better point for handgun loads with power factor is that a heavy bullet at a slower velocity making power factor feels very different than a lighter bullet moving faster to make the same power factor. I won't say that recoil is vastly different, but it does feel very different.
This is a very good point, it raises the question of what is really felt by the shooter. We all know that the bullet is accelerated down the barrel by the powder charge and attains a certain MV, which takes a certain amount of force delivered over a certain amount of time in which to to do this. The shooter feels the same force, as described by Newton's laws, in the recoil. The force comes from the chamber/barrel pressure curve and is proportional to the area under that curve. We also know that the different powders have different burn rates, which means that for any given amount of powder, the pressure curve is going to rise and fall faster or slower depending on the burn rate of the powder. So, lets assume, to accelerate a bullet to a certain velocity takes X amount of total force/energy. But you can vary the degree of acceleration, for instance choosing one powder over another, such that you can get the same force with, lets say, acceleration Y for 1.1 milliseconds, or accelerate at a faster rate Z for 0.8 seconds. Thus, X (proportional to the area under the pressure curve) is equal to either Y for 1.1 millisecond or Z for 0.8 milliseconds. What looks different between the Y and Z pressure curves is the Y curve is going to be taller and narrower compared to the Z curve. The Y impulse recoil is going to hit harder in a shorter period of time than the Z acceleration curve. I don't think anyone holding a firearm can tell the difference in time between 0.8 and 1.1 milliseconds, but they will perceive the difference in the peak impulse pressures, and the faster, higher impulse will feel like more recoil. But in the grand scheme of things, both have the same, net recoil, for the same bullet and muzzle velocity achieved. Power factor determination just takes this up a notch or two because of the bullet weight and velocity changes noted in crbutler's post.