I was just working up some figures on efficiency when crunching my chronograph figures I have compiled this year from many cartridges because I recalled an article I read in one of the gun mags a few years back all about cartridge efficiency- they had a simple equation, muzzle energy/grains of powder. I remember two things from the article, the .308 is top of the line for efficiency in the high power rifle cartridges and the article said the 22 long rifle is the most efficient cartridge (150 foot lbs energy from two grains of powder = 75 ft.lbs energy per grain of powder) BUT the 10mm from my 6 inch barrel is EVEN MORE efficient. I get 1300 fps from 8.5 grains powder pistol with a 180 grainer, that equates to 79 ft-lbs per grain!!!! EVEN MORE then my 357 lever action carbine with 16 inch barrel, that takes 16.7 grains of winchester 296 to push a 158 grain slug 1750 fps, yes impressive BUT only 64 ft-lbs per grain, and this is 16 inc barrel. My load of 8 grains of unique comes out to 76 foot lbs per grain efficiency.