The M6D pistol

he M6D Pistol is an 'up-sized' UNSC handgun issued to Navy officers, this model has been upscaled for use by SPARTAN-IIs in MJOLNIR armor. Even though the Spartan issue pistols are larger than the standard-issue variants (~117%) they can still share magazines. [3] The M6D is a semi-automatic, recoil-operated, magazine-fed, large-bore handgun that is controllable even during rapid fire, although at the cost of accuracy. It is most likely striker-fired, due to there being no visible external hammer. It fires M225 SAP-HE (Semi-Armor Piercing, High Explosive) rounds from a 12-round magazine. Operators can achieve an effective rate of fire of 3.5 rounds/sec or 210 rounds/min. The weapon is very accurate out to its maximum effective range. This accuracy allows incredibly precise target engagement at long range. This, combined with its decent damage against Energy Shields, makes it a viable option when faced with shielded opponents, such as Elites. It is, however, even more effective against unshielded infantry targets, being able to kill most targets in one shot to the head or two to three shots to the body.
The M6D is semi-automatic weapon - this principle of weapon operations means that the weapon will cock itself after every shot due to recoil and will continue to do so until the magazine is empty. The M6D also uses the short recoil principle; it uses the force of the recoil to eject the spent casing, chamber another cartridge, and re-cock the weapon so that it may be fired again. Before the first round can be fired however, a round must be chambered, this is done by inserting a loaded magazine into the grip of the weapon and then by pulling the slide back completely and letting it slingshot forward, which takes a round from the top of the magazine and carries it into the chamber. To reload, the empty magazine must be removed with the magazine release button located on the grip and a fresh magazine inserted. Once the fresh magazine is inserted, the slide is allowed to return to its normal position by the operator. There is no need to re-cock the weapon. Cocking is only necessary when chambering the first round when bringing the weapon out of "safe" mode - safety on, uncocked, unloaded.
The M6D is a very basic pistol compared to most 26th century technology. It is a large handgun, having an overall length of 26.7cm and possesses a rifled barrel, improving accuracy by spinning the bullet. It is issued in a hard chrome finish color and operates like most contemporary pistols. It has rear sights but it does not have a forward sight blade, which is replaced by the smart-link scope. It features a KFA-2 2x optical, smart-linked scope. This scope links directly to a users HUD or a Marine eye piece. It also has a large grip guard, which helps prevent the user from dropping it and a chrome barrel which helps prevent corrosion.I have got this info from halopedia.com