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Terminal.png This article, M921 Asymmetric Recoilless Carbine, was written by Ajax 013. Please do not edit this fiction without the writer's permission.
"Maybe not as precise, or as elegant as the M99CA1, but when it hits somebody, they're going to be washing them off every surface for a week."
―Anonymous UNSC serviceman

M921 ARC
Production information

Asymmetric Recoilless Carbine

Technical specifications
Magazine Size

1 round

Ammunition Type

16mm x 65mm munition/battery hybrid


Asymmetric magnetic acceleration


Accurate to 800 metres/1400 metres with scope


2500 metres


Necros War




The M921 Asymmetric Recoilless Carbine is a UNSC railgun used for anti-structure/materiel/vehicle purposes, being capable of demolishing most targets with ease. While it lacks the high power of magnetic accelerator weapons, it possess a higher rate of fire than similar sized platforms, and with specialised munitions, it can be used to take down a variety of different targets.


The M921 ARC is mainly used by weapon specialists or special forces, when heavy weapons such as the M41B2 Medium Anti-Vehicle/Assault Weapon or M66 Light Multipurpose Assault Weapon are too large, too imprecise or cause too much collateral damage. Being highly accurate, with dialable power settings and a wide variety of munitions for as many situations. Its often used as a substitute anti-armour weapon in urban situations, or special operations that are close to civilians or delicate material that warrant a more controlled weapon. It can also be used as a heavy sniper weapon, capable of eliminating targets without fear of survival. It can use armour piercing, fragmenting, multiple flechette, incendiary and explosive rounds for a variety of purposes. Its also been issued to special forces to specifically eliminate heavy personnel, though this application is often not cost effective, though does cause significant morale issues with the enemy when they witness their comrades being reduced to a bloody mist.

It is most commonly deployed by Special Forces weapon specialists, though sees occasional use with UNSC Army and Marine personnel. Spartans are also exceptionally fond of both its destructive power and high accuracy.


The ARC was used extensively against the Storm Covenant, being capable of killing Elites in a single shot.

The weapon functions by using two magnetics with opposite charges to propel a ferro or paramagnetic slug to high speeds. Due to the nature of its propulsion, it can be exceedingly accurate out to long ranges. The gun is fed by a unique ammunition block, that contains a micro-powerpack good for one shot, and the slug. The rails are produced from high heat resistant materials, allowing it to sustain fire for long periods before it begins to undergo thermal distortion, effecting the accuracy. The rest of the components are high heat resistant polymers, and lightweight alloys optimized and engineered for maximum heat resistance.

The ammunition fired is a 16mm slug, which can fired to a maximum of 11,00 feet a second. While the rounds do not reach the same velocity as the vaunted Stanchion, they cause significant damage on impact thanks to the much heavier weight of the slug. The slug itself comes in a variety of unusual forms, including the normal heavy duty/snub nosed anti-armour round, high explosive, anti-personnel round and other, unusual slugs.

Both rails have Doppler Cooling banks that are made up of an array of tiny LASERs that are arranged in opposite directions. As excited atoms and molecules enter the cooling bank, they gain photons from the laser they are moving away from, via the doppler effect. These atoms then slow to a crawl, due to the cancelling effects of the gained photons and are subsequently chilled. As the barrel continues to heat up, due to thermodynamics, the heat will move from a place of high temperature to a place of low temperature, constantly cooling the weapon until equilibrium is made. As the weapon cools down, the opposite becomes true, with the molecules within the bank moving to warm up the weapon as it drifts below equilibrium. This keeps it closer within optimum parameters but are energy prohibitive.

The ARC's on-board systems, such as the cooling and fire control systems are powered by a hydrogen power pack, in the butt of the gun. This power back is good for 6 days and can be recharged or replaced with modular powerpacks, commonly used in a variety of UNSC gear, and must be replaced as the gun will cease to fire or cool. These packs are small and lightweight, and are non-explosive and non-heat reactive.

The ARC was breech loaded with a combination block of power supply/munition.

Other inbuilt features of the gun include non-electrical controls such as the magazine release and safety, and an advanced fire control system, allowing the power level, and consequently distance to be varied. The fire control system shows maximum range, and predicted penetration of light and hardened materials. The FCS also carries two hardlink ports. Along the upper receiver is a Misriah rail, allowing a scope to be mounted and linked to the FCS, increasing the accuracy of the FCS predictions. The lower receiver also carries a accessory rail, allowing for the mounting of grips or bipods.


The combined powerpack/slug munition packs are available in several different varieties, usually designed for specialised functions.

  • Kinetic Core Penetrator: A snub nosed munition, made of tungsten carbide, the slug is designed to transfer maximum force on impact, smashing armour and vaporising troops with impunity. Such slugs tend to over penetrate both infantry and surfaces making collateral a issue, especially in urban combat scenarios.
  • High Explosive Penetrator: A deadly round, ideal for eliminating infantry, enemy materiel or destroying targets with low chances of collateral. The slug possess a tungsten carbide warhead, then a secondary charge of dense inert metal explosive. This explosive charge consists of a tungsten sheath and an explosive payload resistant to both heat and shock. On impact, a spike is wedged down from the warhead into the explosive, detonating it manually. The small radius explosion is filled with a dense cloud of tungsten microshrapnel, which can shred targets and dismember anybody close to the blast radius.
  • Kinetic Splinter Munition: A unique munition, it consists of seven smaller munitions held in a bundle. After launch, the bundle splinters, and the individual slugs spread out, in an effect similar to buckshot. The effect on targets at short range is devastating, shredding whole teams caught in enfilade fire. It is also destructive against standing structures and light armour.
  • Kinetic Penetrator Incendiary: The KPI fires a round with a tungsten carbide warhead and a Cadmium Telluride polymer core. Upon impact, the heat, pressure and force ignite the CdTe core, which ionizes into a ball of plasma on impact. The resulting conflagration of plasma is enough to incinerate anybody on target, and kill in a short radius, as well as melt holes in armour, or destroy enemy materiel.


M921B ARC "Whiplash"

The Whiplash is an experimental model currently in circulation with Spartan forces for testing and evaluation. The weapon uses a modified bloc with dual slugs and a more efficient battery. This allows for it to quickly charge and fire, then fire a second shot without reload. Unfortunately, due to the prohibitively high cost of each battery, use has bee limited.

M921C2 ARC "Arclight"

A new variant that is currently undergoing trials, it uses new electromagnetic motors to hold a charge near permanently without depleting the battery instantly. Marketed as a sniper-style weapon, that can charge before firing, allowing them to lie in wait and ambush, it has only seen limited testing.

UNSC Comments

Individual and Crew Served Weaponry of the UNSCDF


M6L Personal Defence Weapon System | M57 Pistol | M98 Compact | M19 Modular Pistol

Submachine Guns

M20A Submachine Gun | M12 Special Operations Carbine | M8Z Submachine Gun

Assault Rifles, Carbines, and Battle Rifles

MA6A Individual Combat Weapon System | M2A Carbine | M81 Special Purpose Carbine | M55C Enhanced Battle Rifle

Designated Marksman Rifles

M396 Designated Marksman Rifle | M97 Special Purpose Rifle | M113 Special Purpose Rifle

Machine Guns

M397 Individual Automatic Rifle | M739C Squad Automatic Weapon | M122 Light Machine Gun | M247B2 General Purpose Machine Gun | M247H2 Heavy Machine Gun | AIE-486K1 Heavy Machine Gun | M343A3 Heavy Machine Gun | M780 Special Purpose Machine Gun

Sniper Rifles

M22 Scout Rifle System | M818D Enhanced Modular Sniper Rifle System | M1091 Sniper Rifle System | Sniper Rifle System 99G-S6 Anti-Materiel | M99CA1 Special Application Scoped Rifle | M133 Precision Anti-Materiel Energy Weapon System


M45F Close Assault Weapon System | M108A1 Close Assault Weapon System | M77 Extreme Close Quarters Combat System

Energy Weapons

Weapon/Anti-Vehicle Model 6B Grindell/Galilean Nonlinear Rifle | MX4 Light Support Weapon | M921 ARC

Non-Lethal Weapon

M2 Threat-Negation Device | MX9 Pulsed Energy Projectile System | M39 Long Range Tranquillizer Rifle

Missile and Rocket Launchers

M41B2 Medium Anti-Vehicle/Assault Weapon | M899 Light Anti Armour Weapon | M57 Light Multipurpose Assault Weapon | M1 Multiple Launch Rocket System | M25 Underslung Rocket Launcher

Grenade Launchers

M319N Individual Grenade Launcher | M23 Multiple Grenade Launcher | M363B RPD | M460C Automatic Grenade Launcher | M556 Counter Defilade Grenade Launcher | M24 Underslung Grenade Launcher | M26 Grenade Launcher Module


M71 Mortar | M78 Mortar | M81 Mortar


M117 Light-Weight Field Howitzer

Sentry Guns

M55 GUARD DOG Sentry Gun | M601 GARGOYLE Sentry Gun


M9 Dual Purpose/High Explosive Grenade | M2 Anti-Materiel Grenade | M70 Flash Bang Grenade | M43 Smoke Grenade

Anti-Personnel and Anti-Armour Mines

M320 Anti-Tank Mine | M341 Anti-Tank Mine | M362 Anti-Tank Mine | M121 Bounding Anti-Personnel Mine | M127 Anti-Personnel Mine

Explosive Devices

C-7 Foaming Explosive | C-13 Gertex | C-14 Plastic Explosive | C-15 Liquid Explosive | M303 Thermite Cord | M311 Detonation Cord | M382 Special Munition Attack Charge (Kinetic) | M390 Breaching Charge | M394 Clearance Charge | M404 Special Lightweight Attack Munition | M366 Demolition Charge | M376 Satchel Charge | M379 Explosive Pack

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