MA2B carbine

"Sure, no other subsonic round performs quite like the Nine point Nine, but whoever designed a fully-automatic rifle for it should be fired."

- Anonymous ODST

The MA2B Individual Combat Weapon System, formally known as the SCC-5B in CMA service, is an older model of carbine manufactured for the UNSC. A rare and obscure weapon even within the Special Forces community, the MA2B is designed to provide superior subsonic capabilities without the bulk exhibited by other rifles at the time. It is short and light, with three attachment rails to allow it to be rapidly-reconfigured to mission needs. Unlike its close relatives, the MA2B is chambered with the unique 9.9mm cartridge rather than the more common 6.5mm Unified, which gives it improved stopping power, range, and accuracy when compared to other firearms issued for covert operations.

Development
The MA2B carbine was an old weapon, and it was developed according to the needs of Project ORION in the early Twenty-Fourth Century. Riding high on promising results of animal testing, the Colonial Military Administration's research and development division and the Office of Naval Intelligence began to experiment on the concept of augmented supersoldiers. As the program progressed and predictions became more and more optimistic, the CMA saw an opportunity to upgrade their arsenal to include larger-caliber rifles, as they believed that the final operatives could easily withstand the abuse that such a weapon would have. As they already had a new service rifle being designed for their troops, the organization issued a contract for a subsonic carbine to Misriah Armory in 2318.

Misriah immediately set to work on designing and testing a new range of larger rounds, with each being assessed based on their power, accuracy, weight, and stealth qualities. To assist with the task, the company worked closely with personnel involved in Project ORION, including potential test subjects. Their feedback informed Misriah that their 9.9x65mm cartridge was the most popular, although complaints with its recoil caused them to reduce it to the M94's final length of 46mm.

With the ammunition now finalized, Misriah now began to adapt the design of the new MA2-series assault rifle to fit it. The first resulting prototype, the XMC2-1 designed by Martian-born engineer Knut Danielsen, was formally presented to the CMA procurement officers in 2323. While its built-in suppression system and round performance was impressive, they were thoroughly disappointed with its low rate-of-fire, which was a compromise to allow it to have a near-negligible kick. They requested that this was brought up to par with that of their existing assault rifles, a longer barrel to increase accuracy, and an electronic suite be added so that it could interface with ORION's Advanced Combat Helmet currently under trials. While the latter two were incorporated easily, the former undid their hard work at making it usable by unaugmented soldiers, as fully-automatic fire made it completely uncontrollable. Despite their efforts, these problems persisted into the final rifle that entered service in 2325, mitigated only by a burst-fire option built into the selector switch.

Service history
The MA2B Carbine officially entered service in 2325, just ahead of Project ORION's formal deployment.

Ammunition
The MA2B carbine was the only rifle designed to use the M94 9.9x46mm cartridge. Larger but somewhat shorter than the 6.5mm ammunition typically used in the modern MA5-series assault rifles, the M94 is specifically engineered for use in covert operations within atmospheric environments, without sacrificing the ballistic performance of conventional rounds. To achieve this, it is fin-stabilized to increase range and had a rather heavy tip to defeat most forms of body armor available at the time. Even without the advanced sound-suppression systems found in the MA2B, the M94 is noted as being remarkably quiet, which is why it has also been used in a number of suppressed pistol models.

The M94 was eventually superseded by the improved M104 Special covert cartridge. Introduced in 2495 to serve the second generation of ORIONs, this round is noticeably longer at 54mm to accommodate a larger volume of flashless chemothermal powder. This is paired with a small microcomputer circuit, which controls when the powder is ignited to maintain the bullet's velocity and heading over longer distances. This also means that the round itself can be made 32% heavier without any extra drop or loss of range to improve penetration against armor. The M95 Special was initially too costly to be manufactured en masse, and for a time its production was suspended on these grounds. When the Human-Covenant War began, these issues were resolved and it would fully replace the old M94 stock.

Advantages
In the realm of covert combat, the MA2B strikes a perfect balance between firepower and stealth. The large caliber and high rate of fire ensures that an operator can easily defend themselves in a crowded situation. The integrated sound-suppression system makes it among the most quietest rifles in the UNSC's inventory, with only suppressed pistols proving to be even quieter. It is also remarkably resistant to malfunction, able to operate after being submerged in mud and water conditions that would jam other firearms.