Recoil is momentum conservation: the bullet and propellant gases go forward, so the gun moves back. Heavier guns recoil more slowly and with less energy, which is why recoil is felt less with heavy rifles and why muzzle brakes, which redirect gas, reduce it.
How to use the Recoil Energy Calculator
- Configuration
- Mass of bullet
- Velocity of bullet
- Mass of powder charge
- Gas velocity / bullet velocity
- Mass of firearm
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Pick a typical class to fill in representative values or choose Custom. The powder gas velocity is commonly taken as about 1.5–1.75 times the bullet velocity.
Inputs explained
| Field | What to enter |
|---|---|
| Configuration | Choose one: Light pistol (9 mm class), Large pistol (.45 class), Light rifle (5.56 mm class), Medium rifle (.308 class) … |
| Mass of bullet | Units: g, kg, mg, lb, oz, gr |
| Velocity of bullet | Units: m/s, km/h, mph, ft/s, knots, km/s |
| Mass of powder charge | Units: g, kg, mg, lb, oz, gr |
| Gas velocity / bullet velocity | A number |
| Mass of firearm | Units: kg, g, mg, t, lb, oz |
What each result means
- Recoil velocity of the firearm = ([mb]×[vb] + [mc]×[Gas velocity ÷ bullet velocity]×[vb])÷[mf]
- Recoil energy = [mf]×[Recoil velocity of the firearm]^2÷2
- Recoil impulse = [mf]×[Recoil velocity of the firearm]
- Bullet energy (for comparison) = [mb]×[vb]^2÷2
Example values
How the main result changes when Mass of bullet changes and everything else stays at the example values above:
| Mass of bullet (g) | Recoil energy (J) |
|---|---|
| 4.75 | 17.053 |
| 7.13 | 17.053 |
| 9.5 | 17.053 |
| 11.88 | 17.053 |
| 14.25 | 17.053 |
| 19 | 17.053 |
Formula
V_f = (m_b·v_b + m_c·v_c) / m_f, E_r = ½·m_f·V_f², I = m_f·V_f
Worked example
Inputs — Configuration: Medium rifle (.308 class); Gas velocity / bullet velocity: 1.75.
Results — Recoil velocity of the firearm = 2.7531 m/s; Recoil energy = 17.053 J; Recoil impulse = 12.3887 kg·m/s; Bullet energy (for comparison) = 3,431.875 J.
Key terms
- Free recoil
- The recoil of an unsupported firearm.
Frequently asked questions
Why does a heavier gun kick less?
The same momentum gives a lower velocity and, since energy is p²/2m, less energy.
What recoil energy is comfortable?
Many shooters find under about 15–20 J (11–15 ft·lbf) comfortable in a rifle.
Do muzzle brakes reduce recoil?
Yes – they redirect propellant gases sideways or backwards.
Is this the felt recoil?
No – felt recoil also depends on stock design, fit and the action type.