Recoil

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Introduction

Recoil, and its management, is one of the central issues concerning ballistic weaponry. Every weapon that has the effect of accelerating a projectile experiences recoil as dictated by the conservation of momentum, one of the fundamental principles of physics and laws of nature. Since this subject is touched upon in many other articles, this page is a "quick and dirty" look at the fundamentals of recoil physics, common recoil management strategies of ballistic weaponry, and speculative notes on the recoil of as-yet-to-be-realized weaponry.

Fundamentals of Recoil Physics

As mentioned previously, recoil is a direct result of conservation of momentum. Momentum is the product of mass and velocity vector of an object. A closely related concept is that of impulse, which is derivative (rate of change) of momentum with respect to time, and also the product of the force acting upon an object and the duration it is applied. Conservation of momentum is the observation that, within a closed system, the (vector) sum of all of its constituents remains the same, or in more formal language, is invariant under Galilean transformation under Newtonian physics and Lorentz transformation under relativity. Since for every interaction, the forces acting upon the two objects will always be equal and in opposite directions, and the force will act exactly the same time upon both objects (by definition), if viewed as a system, an interaction cannot create nor destroy momentum, as every change in the momentum of one object is balanced out by an equal change in the opposite direction of another, and thus momentum is conserved.

What this means for ballistic weaponry is that for every meter-per-second added to every kilogram of projectile that is thrown down range by the apparatus of kinematic, the apparatus itself (and its bearer) would be propelled in the opposite direction by the same kilogram-meter-per-second, although it is free to choose to pay it in either currency, mass or velocity. This generalized view on recoil is appropriate in so far as it describes the macroscopic consequence of the "power-level" of ballistic weaponry, but it does not aptly describe the process by which this effect is applied, and thus can miss out on important caveats that is of interest to the science fictional author and audiences.

Recoil for Conventional Guns

The recoil of a conventional gun is, unfortunately, complicated by the use of a propellant (the powder's combustion gas product) to accelerate the projectile. In addition to the momentum of the projectile itself, the conventional gun has to contend with accelerating both the propellant as they combust and chase the projectile, and after the bullet has left the bore, the further acceleration of the propellant gas itself. It is therefore wise to split the discussion of conventional gun recoil into distinct phases, separated by the moment the projectile exits the muzzle.

Note that while we have a relatively decent understanding of the phenomenon that contributes to recoil in the in-bore phase of projectile acceleration, the outflow phase does not admit simple description. What we discuss here will almost assuredly be a gross simplification, especially for the second phase, and the interested reader is always welcomed to consult up-to-date research, preferably of the computerized-fluid-dynamics coupled simulation kind, for the state of the art, if they were so inclined. However, we are confident that this section will still prove to be valuable for the less technically inclined reader.

The In-bore Phase

For a more in depth explanation of the interior ballistic of conventional guns, see this page.

Recoil for Electromagnetic Launchers

(WIP)

Recoil for Lasers

(WIP)

Recoil for Particle Beam Weaponries

(WIP)