How hard does it kick? Enter your load — bullet weight, muzzle velocity, powder charge, and gun weight — and get the free recoil energy (ft·lbf and joules), recoil velocity, and recoil impulse. Built for shooters and reloaders, with honest powder-gas modeling, an inverse solver, and side-by-side load comparison.
Maximum muzzle velocity keeping free recoil energy at or below the limit.
Minimum firearm weight keeping free recoil energy at or below the limit.
Both directions use a 4700 fps rifle gas convention; edit the gas value mentally via the main calculator's custom preset for other conventions.
| Load | 1 | 2 | 3 |
|---|---|---|---|
| Name | |||
| Bullet (grains) | |||
| Velocity (fps) | |||
| Powder (grains) | |||
| Gun (lbs) |
Δ vs load 1 uses exact ratios (difference ÷ load-1 × 100). Gas velocity: 4700 fps rifle convention, powder included.
Typical factory-class loads. Energies are computed by this page's own engine with the stated gas convention — not copied from any table — so they are internally consistent with the calculator above.
Free recoil follows conservation of momentum. The ejecta (bullet + powder gas) carry momentum forward; the gun carries equal momentum backward:
Vgun = (mb·vb + mg·vg) / Mgun
Free recoil energy is then E = ½ · Mgun · Vgun², with the gun mass in slugs (lbs ÷ 32.174). Worked example: 150 gr @ 2700 fps + 50 gr powder @ 4700 fps in an 8 lb rifle → V = 11.43 fps, E = 16.24 ft·lbf (22.02 J), impulse 2.84 lb·s.
No instrument measures gas velocity on your bench; it is an industry convention, and handbooks disagree (roughly 4200–5600 fps across sources). Most online recoil calculators use 4700 fps for rifles, so this tool defaults to it for comparability — with labeled presets for high-velocity rifle (5200), handgun/shotgun (4000), and black powder (2250), a custom input, and a toggle that excludes the gas entirely. Whatever you choose is shown in the results note, never hidden.
Free recoil energy is the physics idealization of the gun moving freely. What you feel also depends on stock fit and shape, recoil pads, muzzle devices, action type, and stance. Use this tool to compare loads objectively — not as a pain predictor.
Free recoil energy is the kinetic energy of the firearm as it recoils, computed from conservation of momentum: the gun's recoil velocity is V = (bullet momentum + powder-gas momentum) / gun mass, and the energy is E = 1/2 × M × V². Example: a 150-grain bullet at 2700 fps with a 50-grain powder charge in an 8 lb rifle produces about 16.24 ft·lbf (22.02 J) of free recoil energy with a recoil velocity of 11.43 fps.
Burned powder becomes gas that exits the muzzle at several thousand feet per second — far faster than the bullet. Even a 50-grain charge at 4700 fps carries meaningful momentum (about 37% of the total in a typical .308-class load), so ignoring it understates recoil. This calculator includes the powder gas by default, with an honest toggle to exclude it.
Gas velocity is an industry convention, not a precisely measured value — handbooks quote anywhere from 4200 to 5600 fps. This tool defaults to 4700 fps for rifles (the convention used by most online recoil calculators), with presets for high-velocity rifle (5200 fps), handgun/shotgun (4000 fps), and black powder (2250 fps), plus a custom input. Pick the closest match or enter your own.
The conservation-of-momentum tool (#1568) is a general physics solver for textbook collisions — it computes generic recoil velocity (m₁v₁/m₂v₂) in kg and m/s. This tool is built specifically for firearms: it computes free recoil ENERGY (not just velocity) using shooter units (grains, fps, ft·lbf), includes powder-gas momentum, and adds inverse solving and load comparison for shooters and reloaders.
No — that is atomic physics (a photon scattering off an electron, tool #1566). Same word, completely different domain. This tool deals only with the macroscopic recoil of firearms.
No. Free recoil energy is a physics idealization — the energy of the gun moving freely. Felt (perceived) recoil also depends on stock shape and fit, recoil pads, muzzle brakes, gas systems, shooting position, and the shooter's body. Two guns with identical free recoil energy can feel very different.
Enter your recoil-energy limit in ft·lbf, then solve in either direction: (a) maximum bullet velocity for your bullet weight, powder charge, and gun weight, or (b) minimum gun weight for your load. Both directions are exact inverses of the same physics, verified by round-trip tests — e.g. feeding 16.24 ft·lbf back in for the 150 gr / 2700 fps / 8 lb example returns 2700 fps and 8 lb.
Inputs accept shooter units (grains, feet per second, pounds) as well as metric alternatives (grams, meters per second, kilograms). Outputs always show both: energy in ft·lbf and joules, velocity in fps and m/s, and impulse in lb·s and N·s.
Boundary note: the conservation-of-momentum tool is a general physics solver for textbook collisions (generic recoil velocity, m₁v₁/m₂v₂, kg and m/s). This page is specifically about firearm free recoil energy — shooter units (grains, fps, ft·lbf), powder-gas momentum, inverse solving, and load comparison.
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