10×31mm

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The 10×31mm is a rimless straight-walled large handgun cartridge designed for use in some of and .
==Cartridge dimensions==
The 10×31mm consists of an 10-millimeter-diameter bullet in a 31-millimeter-long case. The case of the cartridge is rimless.
==Performance==
As a magnum cartridge, the 10×31mm has more than enough power to stop a human-sized target in one shot. While the 10×31mm is less powerful than the larger 12.7×40mm cartridge, it possesses less recoil and its smaller size enables greater magazine capacities in firearms that are chambered for it.
==Cartridge variants==
===Military===
====M135 semi-armor-piercing====
The M135 SAP bullet weighs 11.7 grams (180 grains) and consists of a hardened steel core jacketed in copper. When tested using a 129 mm (5.09 in) barrel from a distance of 40 meters (44 yards), the M135 on-average penetrated 33 centimeters (13 inches) into 10% ballistic gelatin before detonating after passing through (bullets that penetrate at least 30 cm into 10% ballistic gel are considered to be able to reliably produce incapacitating wounds when hitting the chest area on a human target). The M135 is the standard-issue 10×31mm cartridge of the .
====M138 +P+ armor-piercing====
Designed specifically for the with its more robust slide and heavier recoil spring, the M138 +P+ AP bullet weighs 7.5 grams (115 grains) and consists of a dense depleted uranium core jacketed in copper and the cartridge type produces substantially higher muzzle velocities than those of the M135 SAP. When tested from a distance of 40 meters (44 yards), the M138 on-average penetrated 38 cm (15 in.) into the ballistics gel after passing through 63 mm of titanium alloy.
====M337 tactical training round====
The M337 weighs 1.3 grams (20 grains) and consists of a polymer shell holding a powerful liquid anesthetic that also has the ability to immobilize the nano-fibers woven into military training clothes, causing them to harden. The M337 is subsonic and is used specifically for combat simulation training. Due to the M337's substantially lesser energy than non-training ammunition, a special training slide must be used in the pistol to allow for proper cycling.
====M339 stun round====
The M339 weighs 1.5 grams (23 grains) and consists of a less-lethal rubber projectile. Like the M337 TTR, the M339 is subsonic and is used specifically for combat simulation training. Due to the M339's substantially lesser energy than non-training ammunition, a special training slide must be used in the pistol to allow for proper cycling.
====M423 high-explosive squash head tracer====
The M423 HESH-T round possesses a copper jacket with an inert filling at the tip, a plastic explosive that takes up most of the body, a fuse, and a tracer element at the base. When the cartridge is fired, the tracer ignites, leaving behind a visible red trail. On impact, the M423 HESH-T round is "squashed" against the target, and milliseconds later, the fuse detonates the explosive filling. If the infantry target survives, the explosion can stun or disorient the target with concussive force. Multiple consecutive M423 rounds are capable of pinning down heavier infantry such as and . The M423 is able to fully penetrate the of and the with variable consistency, but would be completely stopped by the outer shells of either exoskeleton; therefore, the helmets of the aforementioned suits of armor would protect the wearer from an M423 round to the head, provided the impact is on the titanium shell or thicker plating. Due to the niche purpose it serves, the M423 is warranted to relatively limited use in the UNSC Defense Force. Each M423 bullet is labeled with a white-over-red-painted tip.
====M454 subsonic semi-armor-piercing====
The M454 Subsonic SAP cartridge 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 longer and heavier than that of the other loadings, weighing 23 grams (400 grains), and instead consists of a tungsten core jacketed in copper. An M454 Subsonic SAP round can consistently penetrate a and other types of armor that offer similar levels of protection, but would be stopped by standard-issue body armor worn by UNSC infantry. In order for the M454 round to cycle reliably, a lighter recoil spring akin to those used in civilian pistols must be used for the lower-pressure subsonic load. Each M454 bullet is labeled with a white-painted tip.
===Civilian===
Various ammunition manufacturers make other variants of the 10×31mm cartridge for the civilian or market, such as full metal jacket, hollow-point, and polymer-tipped, the first of which is typically used for target practice, and the latter two of which are mostly used for defense. These civilian market cartridges are typically loaded with much less propellant and generally cannot penetrate adequately-made body armor of the 26th century.
*The M335 Semi-Armor-Piercing High-Penetration round draws inspiration from Lehigh Defense's Xtreme Penetrator ammunition.
*Bert Hsieh and Wendy Lee owned an M6A chambered in 10×31mm loaded with polymer-tipped rounds each weighing 11.7 grams (180 grains) and possessing a muzzle velocity of 350 meters/second (1,150 feet/second).
Category:Weapons