ARC-920 railgun

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

Design details
The ARC-920 railgun is a result of scientific breakthroughs following the Human-Covenant War that allowed for portable, hand-held, electromagnetic launcher systems to be used in combat. The ARC-920's disposable power cell and ferric-shelled M645 FTP-HE projectile has dramatically decreased the weapon's total mass. Despite the ARC-920's lighter weight over previous models, it is still too heavy and cumbersome for general use by non-augmented personnel.

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. The ARC-920 is one of the various limited-production electromagnetic launchers in service with the UNSC Armed Forces, and is widely considered the best among them.

Variants

 * Whiplash: The Whiplash is an improved variant which features a faster charge cycle, two rounds per magazine, and projectiles fitted with a proximity airburst fuse.
 * Arclight: The Arclight is an advanced variant that fires armor-piercing high-explosive rounds capable of piercing through multiple targets at once. While it takes longer to charge the weapon, the charge can be held indefinitely.
 * Extractor: This Railgun has a unique interior green glow.

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 traveling time for a fired shot is almost instantaneous, though still markedly slower than most ballistic, hard light, and laser weapons in the game, which are hitscan. In Campaign and Spartan Ops, the charging time is longer than in War Games.

Advantages
The railgun is extremely powerful and can kill Spartans and all but the highest-ranking Promethean Knights and Elites with one shot. It is also very accurate at short and medium distances.

Disadvantages
The railgun must be charged before firing, which is a disadvantage on the battlefield. It can only fire one slug before reloading and is weak against vehicles. Its lack of scope coupled with its narrow blast radius make it difficult to aim, limiting mostly to firing at stationary or slow-moving targets.

Changes from Halo 4 to Halo 5: Guardians

 * Can now be zoomed in via Smart Scope, which activates the weapon's Projection sight.
 * Like the Gauss turret, it now has hitscan properties.
 * Maximum reserve ammunition increased from 5 to 13.
 * Projectile weakness against vehicles has been removed, leaving it an all around effective anti-vehicle weapon.
 * Charge time is now the same in the campaign as in multiplayer.
 * If the Grunt Birthday Party skull is on, the railgun can now trigger the effects of said skull with headshots to Grunts.

Changes from Halo Wars 2

 * August is the only one that wields an actual Railgun. Despite it being the standard Railgun, she shoots it twice in some occasions.
 * The Railgun does less damage.
 * Extractor Marines wield Railguns in Blitz, the weapon can "siphon" enemies' health and give it to the user & having a higher rate of fire.

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.
 * In addition, the weapon's REQ card in Halo 5: Guardians identifies it as a coilgun.
 * Even though the weapon's name implies a lack of recoil, a railgun or coilgun should still produce substantial recoil.

List of appearances

 * Halo 4
 * Spartan Ops
 * Infinity Briefing Packet
 * Halo: Spartan Assault
 * Halo: Escalation
 * Halo 5: Guardians
 * Halo Wars 2
 * Halo: Battle Born