The AO-63 (Cyrillic: Автомат АО-63) is a Soviet twin-barreled, AK-derived assault rifle chambered for the 5.45x39mm round. It was designed by S.G. Simonov and P.A. Tkachev, and manufactured by TsNIITochMash. It uses a side-by-side barrel configuration, and it can reach a maximum rate of fire of 6000 rounds/min when fired in a two-round burst mode with a 0.01 millisecond delay to increase ballistic performance. This makes it the fastest firing assault rifle known.
The AO-63 assault rifle was used by the Spetsnaz during the Abakan trials in May/June 1986, in search of a more accurate alternative to replace the standard issue AK-74. It was described in the official report as being highly accurate as well as simple and reliable; despite its accuracy and performance, it was later dropped out of the competition for unknown reasons, with the AN-94 emerging victorious.
The AO-63 is a gas operated, 5.45x39mm calibre, AK-derived twin barrel assault rifle. The weapon has side by side barrels with the right barrel predominant, twin rotating bolts/gas pistons and ejects from both sides. The trigger group has a 3 position selector on the right side of the receiver, the first is semi auto firing one barrel, the second in full auto firing both barrels with a 0.01 millisecond delay, the third is unique as at first it fires a two-round 6000 rounds/min burst then one barrel in 850 rounds/min full auto. The magazine is unusual as it has the main double column holding 30 rounds with a single column holding 15 rounds.
In the 1989 film Red Scorpion, a weapon resembling the description of an AO-63 was featured. Many times on the Internet has this weapon been described as the AO-63, although in reality, it was only an FN FAL mockup, with a modified stock, two over/under barrels and a Lewis pan magazine on top of the receiver.