USMC Adopts New Open-tip 'SOST' 5.56 Ammo

After learning that M855 NATO ammo does not perform well from short-barreled rifles such as the M4 carbine, the U.S. Marine Corps has started issuing a new type of 5.56×45 ammo to its troops in Afghanistan. The new SOST (Special Operations Science and Technology) ammo, officially designated MK 318 MOD 0 “Cartridge, Caliber 5.56mm Ball, Carbine, Barrier”, features a different open-tip 62mm bullet. The new bullet, with a lead core (in the top half) and solid copper bottom half, is similar to hunting bullets such as Federal’s Trophy Bonded Bear Claw. The SOST bullet was designed by Federal/ATK, which will produce the loaded ammunition.

The new SOST ammo was first developed for use by SOCOM (Special Operations) in the SCAR rifle, which has a short, 13.8″ barrel. Even in short-barreled rifles, the SOST provides impressive ballistics — achieving 2925 fps in a 14″ barrel. Compared to M855 ball ammo, SOST rounds are more lethal when shot from short-barreled rifles. According to the Marine Times, SOST ammunition delivers “consistent, rapid fragmentation which shortens the time required to cause incapacitation of enemy combatants”. Using an open-tip design common with some sniper ammunition, SOST rounds are designed to be “barrier blind”, meaning they stay on target better than existing M855 rounds after penetrating windshields, car doors and other objects. This is important to troops in the Middle Eastern theater who must engage insurgents inside vehicles or hiding behind barriers.

In Afghanistan, the USMC will issue SOST ammo for both the short-barreled M4 carbine as well as the original, full-length M16A4. The Corps purchased a “couple million” SOST rounds as part of a joint $6 million, 10.4-million-round buy in September — enough to last the service several months in Afghanistan.

M855 Criticized by Ground Troops and Pentagon Testers
The standard Marine 5.56 round, the M855, was developed in the 1970s and approved as an official NATO round in 1980. In recent years, however, it has been the subject of widespread criticism from troops, who question whether it has enough punch to stop oncoming enemies.

In 2002, shortcomings in the M855’s performance were detailed in a report by Naval Surface Warfare Center Crane, Ind., according to Navy Department documents. Additional testing in 2005 showed shortcomings. The Pentagon issued a request to industry for improved ammunition the following year.

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