M921 Asymmetric Recoilless Carbine

The 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. 
==Uses==
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. 
==Operation==
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. 
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.
==Ammunition==
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.
==Variants==
===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==
Category:UNSC Weapons