During the late 1980s, soviet designers developed improved sub-sonic ammunition, suitable for specially designed automatic weapons. These cartridges, known as SP-5 and SP-6, were based on a 7.62×39 M43 case, necked-out to 9mm, and loaded with heavy, streamlined bullets. The SP-5 cartridge was loaded with standard “ball” bullet with lead / mild steel core, and was intended for accurate sniper work out to 300-400 meters. The SP-6 cartridge featured an armour-piercing bullet with hardened steel core, which could defeat typical military type body armour at the ranges of up to 300-400 meters. Two weapons were initially developed for this ammunition, both based on the same receiver and gas operated action – VSS sniper rifle and AS assault rifle. Both weapons were selective fired, with integral sound suppressors, and used same magazines with 10- or 20-round capacity. Latter on, several more weapons were developed for 9×39 ammunition, such as SR-3 and 9A-91 compact assault rifles, used by elite Internal Affairs Ministry, Police and State Security units. The one problem, associated with 9×39, as well as with most other special purpose cartridges, is that such ammunition is usually quite expensive. An attempt was made during late 1990s to produce much cheaper 9×39 AP loading, designated as PAB-9. This cartridge featured bullets with stamped (instead of machined) steel cores, as well as increased driving surfaces. As a result, accuracy was poor and barrel wear significantly increased, so this ammunition was soon abandoned and PAB-9 cartridge is no longer made.
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