The AO-63 is a Soviet two-barrel 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 an over/under barrel configuration, and it can reach a maximum rate of fire of 6000 rounds/min when fired in two-round burst mode, making it the fastest firing assault rifle known.
The AO-63 assault rifle was used by the Spetsnaz during the "Abakan" trials in the mid-1980s, in search of a more accurate alternative to take place over the standard issue AK-74. It was described in the official report as being highly accurate. But overall the AN-94 won among numerous other weapons.
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 mock-up, with a modified stock, two barrels and a pan magazine on top of the reciever.