The AO-63 (Автомат АО-63) is a Soviet two-barrel AK derived assault rifle chambered for the 5.45×39mm round.
It was designed by Sergei Simonov and Peter 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 two-round burst mode with a 0.01 second delay to increase ballistic performance, making it technically the fastest-firing 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.