Popper calibration ammo: 124 gr or 147 gr?

[MarkCO]

I chronographed a bunch of factory ammo. WWB was about 128-131 PF from a variety of 9mms. I found some cheap Greek ammo a few years back that was 121 PF, but out of 100 rounds, had two that were 0PF (squibs).

Energy, or momentum, or conversation of momentum, or conservation of energy, or impulse-momentum, or...there are a LOT of ways to look at the PF/bullet/steel interaction, and most of them are simplified and erroneous. Simple energy nor momentum calculations account for the bullet deformation (plastic and or elastic) and the flex/rebound of the steel, much less the time dependent interaction. Impulse-momentum is probably the closest. I will admit that I ran a bunch of calcs based on bullet hardness, velocity, weight of an AR500 steel at the hinge point and determined the dV of the popper. It was pretty clear that a heavy (and JHPs and soft lead) bullet would drive the steel to a higher velocity than a light (and hard lead and FMJs) bullet at the same PF. A heavy, soft lead, hollow point bullet results in the highest energy transfer (percentage) while a light FMJ results in the least to a popper, given the same PF.

If you want to give the shooter the most benefit, shoot a 95 grain FMJ at 115 PF. If you want to give the shooter the least, shoot a soft lead 160 DEWC at 125.

I choose the 124 at 122 PF because it is accurate, consistent, runs in my gun and provides the equivalent energy transfer of a 115 FMJ at 124PF. I will probably get scolded, but just because an RMI says or does something does not make it right.