A selective fire pistol, the M6I possesses a selector switch allows the user to either fire semi-automatically or fully-automatically. The rate of fire in the M6I's fully automatic mode is about 600 rounds per minute. The M6I typically uses 20-round double-stackmagazines, but 10-round magazines that feed into the M6I do exist. Like the rest of the M6 series, the M6I is short recoil operated, using the recoil left by the previous shot to eject the spent case and load the next round into the chamber. The barrel of the M6I is threaded, allowing the attaching of a suppressor. The M6I can also be fitted with various other attachments, such as tactical lights, smart-linked scopes, and detachable stocks. While the M6I is generally issued in a black polymer finish, a multitude of custom finishes are also available.
Unlike many of the other pistols of the M6 series, the M6I is chambered in a smaller, less-powerful 11.5×34mm cartridge, as opposed to the 12.7×40mm cartridge. The 11.5×34mm is noticeably weaker than the 12.7×40mm, but possesses significantly less recoil, allowing the M6I to be more controllable in automatic fire. Regardless, as a magnum cartridge, the 11.5×34mm is quite powerful itself.
M6Is used by the UNSCDefense Force are most commonly loaded with the M330 semi-armor-piercing high-explosive (SAP HE) rounds. Each of these rounds are made mostly of phosphor bronze, with a cavity filled with a stable explosive. The hard, phosphor bronze layer enables the round to penetrate body armor and enter the target, but is structured to deform shortly after entering in order to prevent the round from exiting the body and causing potential collateral damage. The explosive is then ignited by a fuse, detonating the entire projectile inside the target's body, producing a devastating wound that is crippling if not outright lethal. Each SAP HE round is labeled with a yellow-painted tip.
M335 SAP HP
The M335 Semi-Armor Piercing High-Penetration (SAP HP) is the second most common ammunition type used by the UNSC Defense Force. The projectile is made entirely of phosphor bronze and is machined to have a fluted nose geometry, which not only aids the round in penetration, but also allows it to deliver almost all of its energy into the intended target. Compared to the M330, the M335 sacrifices some potential to deal internal damage in order to improve its ability to penetrate armor and other barriers.
Another, less common military cartridge variant is the M423 high-explosiveconcussive (HEC). Unlike the M330, the M423 only possesses a copper jacket with more explosive filling, which is detonated by an incendiary material at the tip that is first ignited by the round's impact. Instead of penetrating the surface and then exploding inside the target, an M423 round creates a larger explosion at the target's surface, releasing a shockwave that stuns and disorients the target, should he/she/it survive the shot. Combined with the high rate of fire of the M6I, M423 rounds are capable of pinning down heavier infantry such as elites and brutes. The explosion left by an M423 round also serves as a one-way tracer, revealing the location of shot placement while preventing the enemy from leading any projectile path back to the source. Inevitably, the HEC round is less lethal than the SAP HE round and is only effective in specific applications, warranting its relatively limited use in the UNSC Defense Force. An M423 round is labeled with a white-over-red-painted tip.
The 8.3×38mm SLAP is based on the 11.5×34mm necked down to accept a 8.3mm sabot encasing a 5mm Staballoypenetrator. The sabot allows for a smaller, lighter projectile in a relatively large cartridge, resulting in a significantly higher velocity and sectional density when fired. The dense, high-velocity projectile offers very effective armor penetration capabilities, exceeding those of the 7.62×51mm M118 FMJ AP and even the 9.5×40mm M634 HP SAP. Also due to its high velocity and light weight, the 8.3×38mm SLAP possesses a much flatter trajectory when fired, resulting in a greater effective range and better accuracy compared to those of more-standard rounds. Furthermore, Staballoy is pyrophoric, combusting easily at high temperatures. As a result, the 8.3×38mm SLAP is effective at destroying lightly-armored vehicles such as Warthogs and Ghosts; once it pierces plating, it can ignite fuel with the possibility of detonating the entire vehicle. As the cartridge possesses the same overall dimensions as those of the 11.5×34mm, the only adjustment to an M6I that would need to be made in order to accept the 8.3×38mm would be a simple barrel swap.
8.3×38mm Subsonic AP
The 8.3×38mm SubsonicAP is intended specifically to be used in conjunction with suppressors in order to generate as little sound as possible when fired. With the projectile traveling at less than the speed of sound, no sonic "crack" is produced.
In order to compensate for the substantially lower velocity, the subsonic projectile is larger and heavier than that of the SLAP cartridge, and instead consists of a dense tungsten core jacketed in phosphor bronze with no sabot. No amount of mass, however, can fully make up for the substantially lower velocity the Subsonic AP round has when compared to that of the SLAP round; the Subsonic AP cartridge, therefore, possesses inferior armor penetration and wounding capabilities than those of the SLAP. Like the 8.3×38mm SLAP, the 8.3×38mm Subsonic AP possesses the same overall dimensions as those of the 11.5×34mm, so the only adjustment to an M6I that would need to be made in order to accept the cartridge would be a barrel change.
Various ammunition manufacturers make other variants of the 11.5×34mm cartridge for the civilian or law enforcement market, such as full metal jacket and hollow-point, the former of which is typically used for target practice, and the latter of which is mostly used for defense.
The M6I is available in a few additional configurations, each with a distinct model name.
The M6I/U is a larger, up-sized variant of the M6I, possessing a longer grip, allowing it fit in the hands of a SPARTAN wearing MJOLNIR armor while preventing it from using 10-round magazines. It also possesses a longer barrel, which makes the M6I/U slightly more powerful than the standard M6I.
Unlike the standard M6I and the M6I/U, the M6I/B has a five-shot burst mode with a very high cyclic rate of 1200 rounds per minute in place of the fully-automatic function. The M6I/B is otherwise identical to the M6I.
Andra-D054 carries a pair of M6I/Us in her inventory of weaponry, one of which is fitted with a KFA-2 x2 sight and a detachable stock, and both of which are fitted with suppressors and tactical lights. They are nicknamed "Lemon and Lime" for their khaki and olive finish, respectively.
I consider the UNSC's12.7×40mm analogous to the present-day .45 ACP, the former of which is a large, standard-issue handgun cartridge, and the latter of which is a relatively large handgun cartridge that is standard-issue in many modern militaries. I decided to make up a handgun cartridge for the UNSC that would be analogous to the smaller, present-day 9×19mm Parabellum. I settled on basing the dimensions of the cartridge off those of the real-world .454 Casull, as the 12.7×40mm’s dimensions are very similar to those the real-world .500 S&W Magnum. In terms of dimensions, the 11.5×34mm differs from the .454 Casull in that its case is 34mm long as opposed to being 35mm in length, very much like how the 12.7×40mm’s case is 1 mm shorter than the .500 S&W Magnum’s. Another difference between the M6I's 11.5×34mm and the .454 Casull is that the former is rimless while the latter is rimmed.