14.5×114mm

"High velocity, armor-piercing. They'll take the hat off an Elite at two thousand yards. And they ain't cheap."

- Jun-A266

The 14.5x114mm round is used by the United Nations Space Command's Sniper Rifle System 99C-S2 AM and Sniper Rifle System 99D-S2 AMs. At least two variants of this size of round are issued: Armor-Piercing Fin-Stabilized Discarding-Sabot rounds, and High Velocity, Armor Piercing rounds.

Design
A modernized variant of an old ammunition type employed by the Soviet Union during the twentieth century, the round is employed in an anti-matériel role, used to damage or destroy enemy equipment and vehicles. However, thick Covenant armor, and the use of energy shields by Sangheili and Kig-yar, has caused it to take on an anti-personnel role in addition to its anti-armor roles.

The 14.5x114mm round is an anti-matériel munition, meaning that it is specifically designed for use against military equipment rather than against other combatants. It performs rather poorly in this role, as rounds fired at vehicles and equipment will do no damage or ricochet. The round is best used on other combatants depending on their use of body armor and energy shields. The rounds leave behind a noticeable white vapor trail that can reveal the position of the sniper. However, it can be used as an aiming aid for the sniper himself.

APFSDS
The 14.5x114mm APFSDS (armor-piercing, fin-stabilized, discarding sabot) round is a large (in both length and width) projectile, and is equipped with four symmetrical fins spaced equidistantly around the base of the projectile, stabilizing its trajectory. This results in high accuracy, with a hit ratio of 97.3%. The terminal ballistics profile of the 14.5 x 114mm round is impressive: at 600 yards a round will go through about 13 feet of flesh and bone.

The rounds are described as being made of very hard metal, with the core probably composed of tungsten or depleted uranium, like most anti-matériel ammunition. The APFSDS round is an anti-matériel munition, meaning that it is specifically designed for use against military equipment rather than against other combatants.

HVAP
The 14.5x114mm HVAP (high velocity, armor-piercing) round is substantially different to the APFSDS round: While APFSDS rounds are sub-calibre, dart-like projectiles with a breakaway sabot surrounding an arrow-like bullet, HVAP rounds are full-bore rounds consisting of a core of a high-density, hard material surrounded by a full-bore shell of a lighter material such as an aluminium alloy.

HVAP rounds lose velocity and accuracy at long ranges, giving rifles firing this rounf an effective range of roughly 1800 metres, considerably less than the 2300 metre ranges of the later-developed, APFSDS-firing SRS99C-S2 and SRS99D-S2 rifles.

Trivia

 * Currently the term "APFSDS" is reserved for large Tank mounted weapons. In small arms such as the Halo sniper rifles it is called a Flechette.
 * The 14.5x114mm round is actually a Russian heavy machine gun round that was developed for use in anti-tank rifles like the PTRD and PTRS in World War II, later used in Anti-Aircraft and Vehicle-Mounted roles with the KPV; it remains in use to this day.
 * Its armor piercing capability can be seen in a single bullet firing through multiple Spartans and Elites with full Energy Shields.
 * It also bears striking similarity to the 14.5 and 15.2mm APFSDS rounds developed by Steyr-Mannlicher AG & Co KG in the mid 1980's for their AMR 5075 and IWS 2000 sniper weapons.