thumb|Simplified diagram of a multistage coilgun with three coils, a barrel, and a [[ferromagnetic projectile]]

A coilgun is a type of mass driver consisting of one or more coils used as electromagnets in the configuration of a linear motor that accelerate a ferromagnetic or conducting projectile to high velocity.

History

The oldest electromagnetic gun came in the form of the coilgun, the first of which was invented by Norwegian scientist Kristian Birkeland at the University of Kristiania (today Oslo). The invention was officially patented in 1904, although its development reportedly started as early as 1845. According to his accounts, Birkeland accelerated a 500-gram projectile to approximately .

In 1933, Texan inventor Virgil Rigsby developed a stationary coil gun that was designed to be used similarly to a machine gun. It was powered by a large electrical motor and generator.

<math> v_{exit}=\sqrt{\frac{2}{m}{V\mu_0\chi_mn^2I^2</math>

m being the mass of the projectile, defined as kg

V being the volume of the projectile, defined as m<sup>3</sup>

μ<sub>0</sub> being the vacuum permeability, defined in SI units as 4π × 10<sup>−7</sup> V·s/(A·m)

χ<sub>m</sub> being the magnetic susceptibility of the projectile, a dimensionless proportionality constant indicating the degree of magnetization in a material in response to applied magnetic fields. This often must be determined experimentally, and tables containing susceptibility values for certain materials may be found in the CRC Handbook of Chemistry and Physics as well as the Wikipedia article for magnetic susceptibility

n being the number of coil turns per unit length of the coil, defined as m<sup>−1</sup>

And I being the current passing through the coil, defined as A.

While this approximation is useful for quickly defining the upper limit of velocity in a coilgun system, more accurate and non-linear second order differential equations do exist. In 2021, they developed a larger model, the GR-1 Gauss rifle which fired 30-gram steel slugs at up to 75&nbsp;m/s with a muzzle energy of approximately 85 joules, comparable to a PCP air rifle.

In 2022 Northshore Sports Club, an American gun club in Lake Forest, Illinois began distributing the CS/LW21, also referred to as the "E-Shotgun", a compact, 15 joule magazine fed coil gun, manufactured by the China North Industries Group Corp. They project distribution to reach 5000 units per year in the US, and the manufacturer has also unveiled plans to supply the Chinese police and military with units for "non-lethal riot control".

Much higher efficiency and energy can be obtained with designs of greater expense and sophistication. In 1978, Bondaletov in the USSR achieved record acceleration with a single stage by sending a 2-gram ring to 5000&nbsp;m/s in 1&nbsp;cm of length, but the most efficient modern designs tend to involve many stages.

  • Prototype of coil gun. CG42- Full auto coil gun