Hi,
@Tug ~
Interesting thread. Though not appreciated by all, cartridge efficiency is something that many powderheads care about--gun writers being particularly famous for waxing technical about it. Less powder creating less recoil and muzzle flash, ability to chamber in a shorter action, sheer design ingenuity, and other factors that may escape me at the moment.
I confess that, for me, cartridge efficiency has never amounted to the importance that it should perhaps have. I choose my hunting cartridges by the following criteria, in no particular order:
1) Are they chambered in a rifle I want
2) Are reloading components at all available
3) Do they have a time-honored history
4) Do they kill game reliably
My recent fondness for nitro-for-black cartridges makes me a particularly poor exponent of the efficiency fandom. I can't think of cartridges
less efficient than, say, a .500 Nitro For Black or a .450 3.25" Nitro For Black. But I absolutely love the rifles I own in those calibers (which is why I bought them), so there it is. Also, I'll always prefer a .30-06 or .300 H&H over a .308, a 7x57 over a 7 Rem Mag, and, most of all, a .375 H&H over any other more modern rethinking or "improvement" of that most splendid of cartridges.
But like everything big-game-hunting, things that float our boat are a big part of our passion. You are in very good company if cartridge efficiency floats yours, so don't let anyone discourage you from calculating it and making it a criterion for cartridge choice. Ultimately, what counts is that you own the rifles you're happy with, and that you are proud to take them to Africa to make memories with them.