IPSC PF = wt * V / 1000
Where: wt=weight in grains, and V=velocity in fps
Major is from 175 up. 200 gr. .45 bullet at 900 feet/second = 180 power factor.
Minor is from 125 to 174.999. 125 gr. 9mm bullet at 1000 feet/second = 125 power factor.
Adding the caliber to the formula gives us a yard stick for it’s defensive potential. This formula favors bigger calibers, and heavier bullets... But then again - IPSC's formula was weight friendly too and people can moan about hydrostatic shock but that fact is bigger caliber bullets make bigger holes.
Makes sense to me. They also make a lot of noise!