How this calculator works
Use projectile mass, rather than its gravitational weight. The output is classical translational energy at the point where velocity was measured. Air resistance changes speed along the trajectory. Energy alone cannot describe impact behaviour. One grain is exactly 0.00006479891 kg.
Formula
E = m v^2/2; m = 2E/v^2; v = sqrt(2E/m). 1 ft lbf = 1.3558179483314004 J.
Worked example
A 10 g projectile at 400 m/s carries 800 J, about 590.05 ft lbf. At 200 m/s it carries 200 J.
Advertisement
Frequently asked questions
Is muzzle energy constant along the path?
No. Drag generally reduces velocity and energy after launch.
Is a grain a gram?
No. A grain is 0.06479891 g; the optional grain input converts it explicitly.
What does energy tell me?
It describes translational motion. It does not predict penetration or injury.