How Hard Does It Kick? (Recoil)
A plain-English tour of rifle recoil — adapted from Some notes on rifle recoil by Jonathan Spencer BSc — with a calculator that grades the kick in terms your shoulder will understand.
The idea in one breath
When a rifle fires, the bullet and the powder gases rush forward, so the rifle must move backward by exactly the same amount of momentum — that’s Newton’s third law, and it’s the whole story. The paper turns that one idea into three numbers, each telling you something different about the “kick”.
The three numbers that matter
Conservation of momentum gives the fundamental equation, M_gun · V_gun = M_bullet · V_bullet + M_charge · V_charge. Working it through (with weights in grains and velocities in ft/s) yields three handy formulae:
- Recoil impulse —
I = (W_bullet · V_bullet + W_charge · V_charge) / 225400[lb·s]. This depends only on the ammunition, not the rifle. The charge gases travel at roughly 4000 ft/s for smokeless powder, 2000 ft/s for black powder. - Free-recoil velocity —
V = 32.2 · I / W_gun[ft/s], with rifle weight in lb. A heavier rifle moves back more slowly. The old rule: above ~15 ft/s in a 6–7 lb rifle, “gun-head-ache is sure to ensue”. - Free-recoil energy —
E = W_gun · V² / 64.4[ft·lb]. This is the one your shoulder actually feels, and what the verdict below is graded on.
Felt recoil is not only physics: stock shape, butt-plate, the bolt and spring of a self-loader, how firmly you hold, and plain psychology all shift the sensation. The numbers are a fair guide, not a promise.
Worked examples (from the paper)
| Cartridge & load | Impulse (lb·s) | Velocity (ft/s) | Energy (ft·lb) |
|---|---|---|---|
| .223 Rem — 55 gr, 27.0 gr charge, 3240 ft/s, 7 lb rifle | 1.27 | 5.80 | 3.70 |
| 6.5×47 Lapua — 140 gr, 37.3 gr charge, 2614 ft/s, 7 lb rifle | 2.29 | 8.56 | 9.78 |
| .308 Win — 150 gr, 47.0 gr charge, 2820 ft/s, 8 lb rifle | 2.71 | 10.9 | 14.8 |
| .30-06 — 180 gr, 56.0 gr charge, 2700 ft/s, 8 lb rifle | 3.15 | 12.7 | 20.0 |
| .338 Win Mag — 225 gr, 69.0 gr charge, 2780 ft/s, 8 lb rifle | 4.00 | 16.1 | 32.2 |
| .375 H&H Mag — 300 gr, 76.0 gr charge, 2530 ft/s, 9 lb rifle | 4.72 | 16.9 | 39.8 |
The .375 H&H line is for illustration — no one in their right mind shoots a 300 gr load from a 9 lb rifle for fun.
Recoil calculator
Enter a load in imperial or metric units. Results are shown both ways; the verdict is graded on free-recoil energy. Defaults below are a .30-06 deer load.
Enter your load and rifle weight to grade the kick.
How the verdict is graded
| Free-recoil energy | Verdict | Typical company |
|---|---|---|
| under 3 ft·lb (≈ 4 J) | A polite tap | .22 LR |
| 3–8 ft·lb (≈ 4–11 J) | A gentle push | .223 Rem |
| 8–13 ft·lb (≈ 11–18 J) | A firm handshake | 6.5 Creedmoor |
| 13–18 ft·lb (≈ 18–24 J) | A solid shove | .308 Win |
| 18–26 ft·lb (≈ 24–35 J) | A proper mule kick | .30-06 |
| 26–36 ft·lb (≈ 35–49 J) | Newton’s sharp elbow | .338 Win Mag |
| 36–55 ft·lb (≈ 49–75 J) | A charging rhino | .375 H&H |
| 55 ft·lb and up (≈ 75 J+) | Hit by a freight train | .460 Wby, .500 NE |
References: [1] Firearms Fact Book, 3rd ed., NRA (US), 1994. [2] Textbook of Small Arms, British War Office, 1929. Formulae and exemplar values adapted from Jonathan Spencer BSc, Some notes on rifle recoil. Always work up loads from published data — this tool is for understanding, not load development.