The Mark 22 Mod. 0 Heavy Machine Gun is a belt-fed, electronic impulse, electromagnet-assisted delayed blowback-operated 25mm automatic grenade launcher. Firing new proprietary 25x37mm cased-telescoped programmable "smart" grenades at a cyclic rate of fire approaching 300 RPM, the Mark 22 is designed to replace the aging M240ST in providing a ballistic or explosive solution to hostiles, and is capable of suppressing enemies out to 3,000 meters and destroying light armor, low-flying aircraft, and watercraft out to 2,000 meters.
Design
Visually, the weapon resembles a Type 21 Assault Phaser, utilizing the same trigger mechanism and controls. The receiver sits considerably higher than that of the original, and is chambered for belts of lightweight 25x37mm cased-telescoped grenades. Barrel length can vary depending on the model, although the infantry variant maintains a total barrel length of 25 inches including muzzle brake, with an overall weapon length of 55 inches not to be exceeded. The Mark 22 utilizes an advanced attenuated recoil system, which, in tandem with an exoskeleton motor-assisted harness, allows for sustained automatic fire with little felt recoil impulse, and operates on an enlarged electronic impulse-fired delayed blowback action derived from the Mark 15 Adaptive Rifle System. To reduce weight, the battery is mounted externally, underneath the action, and is uparmored to resist shrapnel. The weapon feeds from the left side, although a kit exists to convert it into a left-handed weapon, and it uses a mechanical system to strip rounds from disintegrating link belts. A larger version of the TR-240's backpack can be used to hold up to 250 rounds in a continuous link, with standard belts coming in at 50 rounds each with alternative feed options for conventional drum or stick magazines.
The primary variant issued to select Solas Tempus TACCOM units is the Infantry model, which has weight reduced to roughly 55 lbs and is type-classified as the Mark 22 Mod. 0. A modified Type 21 harness with additional motor assistance units is readily capable of supporting the weight and recoil of the weapon, allowing for highly mobile automatic firepower in situations where a larger, more powerful phaser weapon would be less appropriate. Electronics in the weapon are fully compatible with existing exographic sensor models, and sensor fusion allows for rapid target acquisition and round programming on the fly.
Ammunition
The Mark 22 is capable of firing both programmable airburst-Mark and point-activated rounds with an average muzzle velocity of ~300 m/s. The primary round utilized is the 25mm Mark 942 High Explosive Dual Purpose/Airburst Capable round, popular due to it's effectiveness against the most common threats faced by TACCOM units. When fired in airburst mode, it will read data from the exographic sensor, calculating distance to target and exploding when it reaches behind, over, or to the side of a target, with a kill-casualty radius of 15 meters. In point-activated mode, the round can penetrate through roughly 2 inches of RHA or RHA equivalent, allowing for use against exosuits and light armored vehicles.
A multitude of other rounds exist, although the Mark 942 is the only smart munition currently in service with the Mark 22. These include Mark 943 High Explosive Anti Tank, which is a shaped charge fitted with a standoff rod for penetrating heavy armor, and Mark 944 Flechette, which consists of 24 small flechettes for use against soft targets or when collateral damage must be avoided.
Variants
The Mark 22 is designed to be a flexible-mount heavy machine gun for use on light vehicles, shuttles or aircraft, and exosuits. As such, it is compatible with all mounting Marks, from a light infantry exoskeleton arm to a full-on secured turret mount.
Mark 23 Heavy Machine Gun
For vehicle use, a larger version designated as the Mark 23 (to avoid confusion) is preferred, although a standard Mark 22 is capable of being mounted to any universal "common" systems. Compared to the Mark 22 "Infantry" model, the Mark 23 is significantly heavier at 80 pounds unloaded, and can accommodate heavier or longer barrels for higher endurance or muzzle velocity. Battery size varies, or the weapon's receiver can be hooked up to an external power supply. Rate of fire is tuneable on the Mark 23, unlike the 22, and a larger electronically-boosted feed mechanism allows for maximum cyclic rates of fire approaching 1000 rpm. It feeds from a belt, and has brackets to accommodate multiple ready magazines that can be changed on the fly. The vertical grips are usually absent on 23s, and the straight grip/trigger are usually replaced by a set of spade grips. Ladder sights, electronic targeting assists, and HUD-cuing devices can be attached by means of an optional rail on top of the feed cover.
Currently, a quartet of Mark 23s on universal Twin Combat Module (TCM) mounts can be found on TX88.