ARC-920 railgun

The Asymmetric Recoilless Carbine-920, abbreviated ARC-920 or known simply as the railgun, is a compact-channel linear accelerator weapon used by the United Nations Space Command. It was designed and manufactured by Acheron Security.

Design details
The ARC-920 uses a pair of parallel conducting rails to accelerate its projectiles. A large electric current flows from one rail into the projectile and then to the other rail; the electromagnetic effects of this interaction accelerate the projectile to an immense speed. The rifle requires a brief charging period before firing high-explosive rounds accelerated to an incredible speed. The explosive yield contained in the round adds to the kinetic force of the impact, making the weapon effective against both infantry and armor. The weapon lacks a scope.

Gameplay
Compared to the Spartan Laser, the ARC-920's charging time is half the duration and deals less damage to vehicles. In addition, the travelling time for a fired shot is almost instantaneous. In Campaign and Spartan Ops, the charging time is longer than in War Games.

Tactics
Even though the weapon lacks a scope of its own, one can zoom in using the armor's built-in 5x zoom function, and the weapon can be charged and fired with the zoom only being broken by the shot firing. This can be used to give greater precision to long-range shots. This tactic is only effective against stationary, very large, or slow-moving targets, however. Against more nimble targets the ARC-920 is best used at close to medium ranges, where its non-line-of-sight charge-up and significant aim-assist make it quite deadly. The long reload between shots however can make it a punishing weapon to use if the first shot misses, since the user will be defenseless for a fairly long while before another railgun shot is available, and will be forced to retreat or switch to another weapon. Additionally, the weapon has a very small splash radius and has a very high projectile speed, so unlike most other explosive weapons it is best used by aiming directly at the center of mass of the target as opposed to firing at the ground below them in order to kill via splash.

The railgun is primarily an anti-heavy-infantry weapon, capable of killing Spartans, Elites and, on any difficulty below Legendary, even Promethean Knights in a single hit, but it also has some limited anti-materiel capability - it can kill Ghosts in two hits, and Banshees or Warthogs in approximately three. Against heavily armored vehicles such as Scorpions, Wraiths and Mantises it is not very effective, unless the vehicle in question has already been severely damaged by other means.

In Spartan Ops, the ARC-920 features an additional advantage in the fact that, unlike the Spartan Laser, Rocket Launcher and Sniper Rifle, a player can pick up additional ammunition from all UNSC ammo crates, giving the player a potentially unlimited supply of ammunition.

Trivia

 * Canonically, a magnetically accelerated projectile would move at many times the speed of sound. However, for the sake of balance, the railgun's projectiles move at a much slower subsonic speed in gameplay.
 * Despite being a railgun, the rings that form around the barrel when charging, as well as the Railgun Kill medal depicting a projectile going through rings, seem more indicative of a coilgun.
 * This weapon's name may be a reference to the M-920 Cain, a railgun in the Mass Effect series. In addition, the number 920 is a reference to the number 7 (9-2-0=7)

List of appearances

 * Halo 4
 * Spartan Ops
 * Halo: Spartan Assault
 * Halo: Escalation