The Simonov AO-63 was a double-barreled assault rifle engineered in the Soviet Union during the mid-1980s. The design incorporated an "over-under" barrel arrangement which gave it a very unique appearance in the world of assault rifles. Otherwise, the general configuration of the rifle was conventional, featuring a shoulder stock, shrouded forend and pistol grip. The AO-63 was chambered for the intermediate 5.45x39mm cartridge and fired from a standard 100-round drum magazine. Additionally, the weapon could accept a 30-, 40- and 45-round AK-74-style curved detachable box magazine. Design work occurred in 1986 and was attributed to Sergei Simonov prior to his death that same year. Additional work was handled by Peter Tkachev to which the working model was produced through the Russian TsNITochMash industrial bureau.
Published numbers regarding the AO-63 design include an overall weight of 3.68 kilograms with an overall length of 890mm. The internal action was of a conventional gas-operation to which a rate-of-fire between 850 to 6,000(!) rounds-per-minute could be reached. While an impressive statistic, nothing was said of barrel cooling or the abuse undertaken by the internal action - issues that would naturally present themselves over a period of time. Overall range was listed out to 1,000 meters though effectiveness was generally met within 600 meters.
The Soviet/Russian special forces group - SPETSNAZ - briefly evaluated the AO-63 in attempting to replace its less accurate 5.45x39mm AK-74 line of assault rifles. However, the more conventional 5.45x39mm AN-94 was eventually selected and the AO-63 fell to history. The AN-94 began service in 1997 and continues to gradually replace the large numbers of AK-74 currently in Russian military service.
A mock up of the AO-63 appeared in the 1989 Dolph Lundgren vehicle "Red Scorpion". This example was really a South African R1 (a local variant of the Belgian FN FAL) heavily modified for screen time with only the lower barrel being made to fire.