ps. Most of these formulas take for granted that you have the right bullet for the job in hand.
Yes, and yet there are a lot of differences in bullets, and how they perform on game.
For an example, I can load a 145 grain Speer SPBT on top of a dose of IMR4350 in my 7mm mag to have a nice load for deer and antelope. I've proven this load many times, and it's never failed to perform perfectly for me.
But if I switch bullets to a Speer 145 grain Grand Slam on top of the same load, I'm perfectly able to take animals the size of elk and bison. I've used it enough to know it works, and works well.
The only difference in the load is the type of bullet used, yet the terminal ballistics of the load are somewhat different. The SPBT expands quicker, so is better suited to lighter game. The Grand Slam is designed for deep penetration through controlled, slower expansion, which allows larger animals to be taken.