The 14.5x114mm Armor-Piercing Fin-Stabilized Discarding-Sabot bullet is used by the United Nations Space Command's Sniper Rifle System 99C-S2 AM and Sniper Rifle System 99D-S2 AMs. Possibly similar to an ammunition type employed by the Soviet Union during the twentieth century, the round is employed in an anti-material role, used to damage or destroy enemy equipment and vehicles. However, thick Covenant armor, and the use of energy shields by Elites and Jackals, has caused it to take on an anti-personnel role in addition to it's anti-armor roles.[1][2]
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.[3]
In-game, the 14.5mm sniper round is massively underpowered. The fact that Covenant life-forms can realistically survive a hit from such a powerful round is debunked by the fact that the bullet travels through the body and can hit another enemy. If that were the case, the round should leave a massive, gaping hole in the body, undoubtedly killing or seriously wounding the enemy combatant.