Simply stated, mass and velocity are the
only contributors to energy. The basic formula is as follows:
Let's compute using the data from the two disparate rounds (180gr, 985f/s). The first step is to convert to standard metric units, otherwise we'll have a ton of base conversions to deal with throughout.
- 180 gr = 0.0116638 kg
985 f/s = 300.28 m/s
With these figures, we can compute the energy in joules, which can then be converted to foot-pounds.
- E = 0.0116638/2 * 300.28^2
E = 0.0058319 * 90168.0784
E = 525.8512164209599 J
J = 0.7375622 lb/ft
E = 387.8479672 lb/ft
As you can see, Speer is somewhat unrealistic in their figures. It has nothing to do with powder burn rates, bullet shape, the alignment of the planets or even the price of tea in China. It's physics, pure and simple.