During Religious Emphasis Week in 1956, our forestry-school class invited a local rabbi to explicate Judaism. He asked "Which Judaism?" and explained that "wherever there are two Jews, there are three opinions" about everything.
Seems that the same is true about shooters and cartridge efficiency. In Hatcher's Notebook, the general explained that the efficiency of a cartridge is the ratio between (a) the theoretical chemical energy stored in the powder and (b) the kinetic energy delivered by the speeding bullet. The actually delivered energy is such-and-such a percentage of the theoretically stored energy. That's the old more-or-less "official" or technical definition of a cartridge's efficiency.
Other shooters define cartridge efficiency in their own terms � especially when they're talking about relative effectiveness and calling it "efficiency."
To calulate efficiency as General Hatcher defined it, first calculate the chemical energy stored in the powder charge � charge weight in grains times (IIRC) 178 foot-pounds per grain (for IMR powders). Then calculate the percentage of that theoretical total energy that the traveling bullet actually delivers.
Don't be surprised to find that some of the most efficient cartridges are the least effective � the .22 Long Rifle versus the .458 Winchester Magnum, for example.
