Below is a transalated report of the Abakan assault rifle trials. Various weapons were tested with the AN-94 being the winner, but another rifle listed as the "AO-63", Designed by Simonov & Tkachev fired around 6,000RPM when the 2-round burst mode was selected. Does anyone here know this rifle?.
PS: The AO-63 is listed here below as the "SC-63"
Original Sources: http://translate.google.co.uk/translate?hl=en&sl=ru&u=http://www.sinopa.ee/sor/bo001/bo04av/bo04av03/01abakan/abakan.htm&sa=X&oi=translate&resnum=2&ct=result&prev=/search%3Fq%3D%25D0%2590%25D0%259E-63%2B5,45%26hl%3Den%26sa%3DG
http://slovari.yandex.ru/dict/guns/article/guns/guns-067.htm