So, after coming up with some interesting neat way to calculate bullet power I forgot it and didn't write it down.
Now in my old age I came up with this: fps X ft lbs / grain weight = force factor (move decimal to make it a two whole number expression)
I'm trying to compare various cartridges to see which has the better overall performance with quick calculations and yes reams of paper and a computer app would do that. Say I'm attempting to choose which would be best of a limited number of possible long term success cartridges.
Grab the existing info for that cartridge, feet per second at the muzzle, times the foot pounds of force gets you a number representing power, then divide by the grain weight of the bullet to "temper" the power by mass. Move decimal to make it workable.
This is basically "fudge factor" math, not existential truth discovery. Take a 115 grain bullet at 2500 fps with 1700 ft lbs of force - a 6.8SPC recipe. Do the math you get 36,956 or 36.9. Now a 5.56 recipe, 55 grain bullet running at 3200 fps with 1,300 ft lbs, you get 75.6.
For some perspective, .375 SOCOM runs a 200 grain bullet at 2,500 fps carrying 2,500 ft lbs, which results in 31.2.
Now we have three data points (all AR15 rounds) and you can line them up: .375 SOCOM at 31.2, 6.8SPC at 36.9, and NATO 5.56 at 75.6.
What does this tell you?
Which one you could use for a particular game when hunting (or target shooting). I'm beginning to see an exponential scale with this, as the mass and power get larger the number slowly gets smaller. Easy to say "low numbers better than large numbers" but then trajectory comes in and bullet drop for the range involved needs to be considered. I might dream up that magic some day. I was looking for some way to compare what cartridge might be more appropriate with some kind of number to make it seem as if there is science behind it.
Like that happens, I want the .375 because it's a big honking cartridge that barely fits in the magazine single stack. Looks impressive, for the money these days I'm in for less than the 6.8 ten years ago. Such is life.
Maybe there is some way to factor in the range where it still has 1,000 ft lbs. That gives you it's ethical limit which is something we could consider more often.
Have fun with that when you need to sort out some idea of where to go with competing cartridges.