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 is an older model of carbine manufactured for the UNSC. A rare and obscure weapon even within the UNSC's Special Forces, 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 P/N 16309 attachment rails to allow it to be rapidly-reconfigured to mission needs. Unlike its close relatives, the MA2B is chambered with the unique M94 9.9mm cartridge rather than the more common, which gives it improved stopping power, range, and accuracy when compared to other firearms issued for covert operations.

Ammunition
The MA2B carbine was the only rifle designed to use the M94 9.9x46mm cartridge. Larger but somewhat shorter than the 7.62mm 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The M94 was eventually superseded by the improved M95 Special covert cartridge.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 arrived, 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.