Gun Recoil Energy Calculator
Free recoil energy in ft-lbs and joules, plus recoil velocity and momentum, from bullet weight, muzzle velocity, powder charge and gun weight. How it works
Use the Gun Recoil Energy Calculator
About the Gun Recoil Energy Calculator
A 150 gr .308 Win bullet at 2800 fps over 45 gr of powder gives 15.81 ft-lbs of free recoil in an 8 lb rifle, and 21.08 ft-lbs in a 6 lb one. Energy = (bullet weight × muzzle velocity + 4700 × powder charge)² ÷ (64.348 × gun weight), with weights in pounds and 4700 ft/s an assumed speed for the powder gas. It is the energy of the gun moving back freely, not the felt recoil at your shoulder.
Free recoil for the calculator’s preset loads
| Preset | Bullet weight | Muzzle velocity | Powder charge | Gun weight | Recoil energy | Recoil velocity | Recoil momentum |
|---|---|---|---|---|---|---|---|
| .22 LR | 40 gr | 1200 fps | 1.5 gr | 5 lb | 0.19 ft-lbs | 1.57 ft/s | 7.86 lb·ft/s |
| .223 Rem | 55 gr | 3240 fps | 26 gr | 7 lb | 4.09 ft-lbs | 6.13 ft/s | 42.91 lb·ft/s |
| .308 Win | 150 gr | 2800 fps | 45 gr | 8 lb | 15.81 ft-lbs | 11.28 ft/s | 90.21 lb·ft/s |
| .44 Mag | 240 gr | 1180 fps | 24 gr | 3 lb | 16.58 ft-lbs | 18.86 ft/s | 56.57 lb·ft/s |
| 12ga | 437.5 gr | 1300 fps | 28.5 gr | 7.5 lb | 20.88 ft-lbs | 13.38 ft/s | 100.39 lb·ft/s |
| 9mm Luger | 124 gr | 1178 fps | 4.9 gr | 1.56 lb | 5.81 ft-lbs | 15.49 ft/s | 24.16 lb·ft/s |
| .45 ACP | 230 gr | 958 fps | 6.9 gr | 1.83 lb | 11.07 ft-lbs | 19.73 ft/s | 36.11 lb·ft/s |
| 5.56x45 NATO | 55 gr | 3323 fps | 23.5 gr | 6.7 lb | 4.07 ft-lbs | 6.25 ft/s | 41.89 lb·ft/s |
| 7.62x39 | 123 gr | 2388 fps | 27.3 gr | 6.7 lb | 8.43 ft-lbs | 9.00 ft/s | 60.29 lb·ft/s |
The first five rows are example inputs behind the Common Calibers menu, not published data; 437.5 gr is a 1 oz shot charge. The last four take bullet weight, velocity and powder charge from the maximum load of one bullet and powder in the Vihtavuori Reloading Guide 2024 (Lapua 124 gr FMJ-RN over N330; Sierra 230 gr FMJ over N330; Hornady 55 gr FMJBT over N130, from the .223 Remington table, as the guide has no 5.56 NATO table; Lapua 123 gr FMJ over N120), and the gun weight from the maker: a Glock 17 Gen5 (708 g) and a Glock 21 Gen4 (830 g) with an empty magazine, and a Ruger Mini-14 Ranch Rifle and Mini Thirty (6.7 lb each). Change any input to match your own load and firearm.
The .308 Win preset load in rifles of different weight
| Gun weight | Recoil energy | Recoil energy (J) | Recoil velocity |
|---|---|---|---|
| 6 lb | 21.08 ft-lbs | 28.58 J | 15.04 ft/s |
| 7 lb | 18.07 ft-lbs | 24.50 J | 12.89 ft/s |
| 8 lb | 15.81 ft-lbs | 21.44 J | 11.28 ft/s |
| 9 lb | 14.05 ft-lbs | 19.05 J | 10.02 ft/s |
| 10 lb | 12.65 ft-lbs | 17.15 J | 9.02 ft/s |
Every row uses a 150 gr bullet at 2800 fps with 45 gr of powder. Momentum is 90.21 lb·ft/s throughout; only the gun weight changes.
Gun weight for a target free recoil with each preset load
| Preset | Recoil momentum | 10 ft-lbs | 15 ft-lbs | 20 ft-lbs | 30 ft-lbs |
|---|---|---|---|---|---|
| .223 Rem | 42.91 lb·ft/s | 2.86 lb | 1.91 lb | 1.43 lb | 0.95 lb |
| .308 Win | 90.21 lb·ft/s | 12.65 lb | 8.43 lb | 6.32 lb | 4.22 lb |
| .44 Mag | 56.57 lb·ft/s | 4.97 lb | 3.32 lb | 2.49 lb | 1.66 lb |
| 12ga | 100.39 lb·ft/s | 15.66 lb | 10.44 lb | 7.83 lb | 5.22 lb |
Gun weight = momentum² ÷ (64.348 × target energy), the calculation behind the table under the result. The momentum of a load does not depend on the gun, so a heavier gun is the only way to lower free recoil without changing the load. A weight below what the gun really weighs means the load already recoils less than the target.
Methodology
Metric inputs are converted to grains, fps and pounds before the formula runs (1 g = 15.4323584 gr, 1 kg = 2.2046226218 lb), and every result is also shown in joules, m/s and kg·m/s. The gauge bar sorts the energy into this page’s own comparison bands, Mild (under 5 ft-lbs), Moderate (5 to 15), Heavy (15 to 30) and Extreme (30 and up); they are not a published scale.
How to use this tool
- Choose Imperial (grains, fps, lb) or Metric (grams, m/s, kg). Numbers already typed are converted to the other units.
- Enter bullet weight, muzzle velocity, powder charge and gun weight, or pick a preset under Common Calibers to fill all four.
- Use the weight of the firearm as fired, with scope, sling and loaded magazine. Every extra pound lowers the result.
Frequently asked questions
- Is free recoil the same as felt recoil?
- No. Free recoil is the energy of the gun moving backward if nothing held it, worked out from the momentum of the bullet and the powder gas. Felt recoil is what you notice at the shoulder: it also depends on stock fit, the recoil pad, a muzzle brake, a gas action and the shooter, and no formula gives it.
- How much recoil does a .308 have?
- With the calculator’s preset (150 gr, 2800 fps, 45 gr of powder), an 8 lb rifle has 15.81 ft-lbs of free recoil and a 6 lb rifle has 21.08 ft-lbs. Your figure depends on the actual load and the weight of the rifle.
- How heavy does a rifle need to be for less recoil?
- With the .308 preset load, 12.65 lb for 10 ft-lbs of free recoil, 8.43 lb for 15 ft-lbs and 6.32 lb for 20 ft-lbs. The momentum of the load is fixed, so energy falls in proportion to gun weight: going from 6 lb to 9 lb cuts it from 21.08 to 14.05 ft-lbs.
- What does the 4700 in the recoil formula mean?
- It is the assumed average velocity of the powder gas leaving the muzzle, in ft/s. Outdoor Life prints the formula with 4,700 as Hodgdon’s, a Sporting Shooter column uses 4,000, and the worked 7×57 mm example in Wikipedia’s free recoil article uses 5,200 ft/s. In the .308 preset the gas carries 30.21 of the 90.21 lb·ft/s, a third of the momentum, so the figure chosen moves the result.
- Is recoil energy the same as recoil momentum?
- No. Momentum (lb·ft/s) is what the load delivers and does not depend on the gun. Energy (ft-lbs) is that momentum squared, divided by twice the mass of the gun, so it drops as the gun gets heavier.
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