Energy = mass x force x time
Mass is the weight of the bullet in grains divided by 7000 grains per pound times the acceleration of gravity (32 feet per second).
M = (weight of bullet grains / 7000 grains) X 32 ft / second
Time is a function of barrel length and is usually in parts of a second. For the purposes of this class, we will typically use whole numbers, therefore exaggerating the effect of time.
Here is an example of the formula in action, finding Energy.
Mass = bw/7000 x 32 and bullet weight (bw) is 519.32 therefore 519.32 divided by 7000 and times 32 (in that order) gives us a Mass = 2.37. Force is 5814 and Time is 1.38 seconds.
Summary: M = 2.37 F = 5814 T = 1.38
E = 2.37 X 5814 X 1.38
E = 19047.69