M6J Carbine

The M6J carbine (more formally, Carbine, Calibre 12.7 mm, M6J) is a UNSC-made pistol-calibre carbine operating on the short recoil principle manufactured by Misriah Armoury. The M6J fires the 12.7x40mm cartridge, a semi-armour-piercing round that gives the carbine superior stopping power but without the risk of over-penetration.

In addition to power, the M6J is designed to be rugged and reliable, and pistols are able to remain operational after long periods without cleaning, Slipspace transitions, high-g aerial manoeuvres, and excessive fouling of parts by foreign matter.

History
The M6J was adopted in 2531 after requests for a new carbine by the UNSC Special Operations Command, who found the MA2B's performance to be unsatisfactory against shielded Covenant soldiers. The Navy and Marine Corps chose to adopt the MA5K carbine, looking for cartridge and parts compatability with the standard-issue MA5 rifle.

The Army, in contrast, adopted the M6J carbine, which had been derived from Misriah from their popular M6 pistol series. From experience, the Army knew that their SOCOM forces relied heavily on their pistols in the intense urban and room-to-room combat that characterised the Great Wars. As a result, they looked for a carbine that provided parts and ammunition compatability with the M6. Misriah's M6J allowed this, and even allowed a standard-issue M6G to be converted into the carbine.

Design
The M6J is blowback-operated: Energy to operate the firearm's various mechanisms and provide automation is derived from the movement of the spent cartridge case pushed out of the chamber by rapidly expanding powder gases. This rearward thrust, imparted against the bolt, is a direct reaction of the total reaction to the forward thrust applied to the bullet and the expansion of propellant gases. The extremely high recoil created by firing the 12.7mm rounds is reduced by an advanced articulated mechanism which allows the block and bolt to recoil off-axis into a recess behind the weapon's magazine well, as well as the barrel being in line with the shooter's hand, which reduces felt recoil and muzzle climb by eliminating the distance between the shooter's hand and the bore axis. This, the sheer weight of the firearm, the use of self-molding plastasteel grips, the forward balance, a detachable shoulder stock, and a muzzle brake offset recoil by nearly 50%.

The M6J features a 355mm barrel, which is threaded, allowing it to accept suppressors, and mounts four sets of Picatinny Combat Attachment Points for the attachment of optics, aiming modules, or ancillary weapons. The bore and chamber are plated with chromium, a feature usually seen only in assault rifles. This plating dramatically increases the life of these parts by resisting corrosion and wear. Due to this, and the abundant use of titanium in the weapon's design, the weapon requires zero cleaning or lubrication, though Misriah states that cleaning is required after 10,000 rounds. These features, as well as generous clearances between moving parts allow the M6J to endure large amounts of foreign matter and fouling without failing to cycle. The M6J can survive exposure to temperatures ranging from -140 to 160 degrees Celcius, being soaked in salt water, being dropped repeatedly on concrete, and being buried in sand, mud and snow. Additionally, the M6J proves a MRBF (mean rounds before failure) of 200,000 rounds.

The M6J features multiple internal safeties including a trigger block, that prevents the trigger from moving without being pulled, and a circuit breaker that prevents the electronic firing system from conducting electricity when engaged. The M6J also has an ambidextrous external safety lever allowing both left and right handed people to comfortably engage the safety mechanism. Rounds are electronically-fired, preventing jams or malfunctions caused by breaking firing pins. The M6J is available in three different finishes: hard chrome, black polymer, and electroless nickel. Like the rest of the M6 series, it features a large trigger guard, which helps prevent the user from dropping it. A self-molding plastasteel grip provides more comfort while firing. The pistol carries adjustable, concealable iron sights, and a detachable shoulder stock.

Due to its relatively-shallow magazine, the M6J features only semi-automatic and burst-firing modes in order to conserve ammunition. Ammunition is fed from a thirty-three-round quad-column casket magazine, which can hold a great amount of ammunition while retaining the length of a standard magazine, although wider. The M6J fires the 12.7x40mm round, giving it incredible stopping power and the ability to pierce body armour, though it does have a tendency to drop casings on the wielder's foot, leading some UNSC personnel to favour the M7/Caseless Submachine Gun. Two variants of ammunition are available; the most-often-issued round is the M225 Semi-Armour-Piercing High-Explosive cartridge. The round combines both an armour-piercing capability and a high explosive effect. The initial impact ignites a small quantity of incendiary material in the tip, triggering the detonation of the HE charge, thus blasting a path through the armoured target for the penetrator. The remaining element of the round is the tungsten penetrator. This has a large amount of kinetic energy and will penetrate the now-unarmoured target through the path created by the explosive. A pre-cut cross on the tip of the penetrator makes the bullet expand inside the body, increasing its diameter to limit penetration and produce a larger diameter wound. The triggering of the explosive charge is dependent upon the resistance of the target. If the target offers little resistance then the lack of frictional heating will prevent the incendiary from igniting and the high explosive from detonating, preventing collateral damage. A rarer type of ammunition is the M228 Semi-Armour-Piercing High-Penetration cartridge, which allows for superior armour penetration, but without the risk of overpenetration and injuring civilians. The bullet is jacketed with copper-coated titanium and tipped and cored with tungsten. Upon striking body armour, the jacket penetrates before deforming, and will temporarily help maintain the shape of the projectile so that it has a better chance of penetration. A second impact against bone or solid muscle mass inside the target's body will complete the jacket's rupture, at which point the projectile mushrooms and fragments into smaller pieces, causing a large number of wound channels and maximising damage. All these ammunition types are available in red, green, blue, or infrared tracers, which feature a delay element to prevent the filler from igniting until it is some distance away from the shooter, allowing him to be better concealed.

The M6J is designed for modularity and and ammunition compatability with the M6. As a result, an M6G pistol can be easily converted into an M6J with the addition of a carbine-length barrel, a blowback-operated bolt, and a stock that attaches to the pistol frame.

Operators

 * United Nations Space Command
 * Unggoy Star Empire
 * Various New Covenant successor states