Muzzle / Downrange Energy & Momentum
Kinetic energy and momentum from bullet weight and velocity.
How this works
Momentum (lb·s) = bullet weight (gr) × velocity (fps) ÷ 225,218
These are the standard physics formulas for kinetic energy and momentum, simply converted into the units (grains and feet per second) that hunters actually measure ammunition in. The 450,240 and 225,218 constants fold the grain-to-pound and unit conversions into one number.
Energy vs. momentum
Energy scales with velocity squared, so faster, lighter bullets look impressive on paper. Momentum scales with velocity to the first power, which is part of why heavier, slower bullets are often favored for deep penetration on tougher game — momentum tracks more closely with how well a bullet keeps driving through tissue and bone.
Frequently asked questions
What's a "good" muzzle energy for deer hunting?
Most state minimums for deer sit somewhere around 1,000 ft-lb at the muzzle, though the actual legal minimum (where one exists) varies by state and weapon type. Many popular deer cartridges deliver 1,500–2,500 ft-lb, well above typical minimums.
Why does energy matter more than velocity alone?
A very light, very fast bullet and a heavier, slower one can carry the same energy — energy is what actually does the work of the shot, which is why it's the number most state regulations and hunting guides reference rather than velocity by itself.
Is momentum the same thing as energy?
No — they're related but different. Energy scales with velocity squared while momentum scales with velocity directly, which is part of why a heavier, slower bullet can penetrate similarly to a lighter, faster one with the same energy figure.
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