You can calculate variables in the Foot Pound formula with this page. You put in bullet weight (in grains) and speed ( in feet per second ) and click for Foot Pounds of Energy delivered at muzzle. You can see if heavier bullets for game really have more knock-down power. Sometimes the heavier bullet is so much slower, it's not more, but less. Find out this way. The formula is Energy = Weight times Velocity Squared divided by 450395 (fixed constant).