BARS replaces a traditional gas piston system,  named after the creator of which weapon?
AL-7:  The AL-7 uses a type of operation developed by Pyotr Tkachyov of TsNIITochMash (Central Institute for Precision Machine Building) in the mid-1960s known as "Balanced Automatics" first used on the AO-38 assault rifle. AL-7:  The Balanced Automatics Recoil System (BARS) replaces the traditional Kalashnikov gas piston operating system, reducing the negative effects of recoil and allowing more efficient use of automatic fire. AK-47: The AK-47, or AK as it is officially known (Russian: Автомат Калашникова , "Avtomat Kalashnikova ", 'Kalashnikov's Automatic Rifle' ), also known as the Kalashnikov, is a selective-fire (semi-automatic and fully automatic), gas-operated 7.62×39mm assault rifle, developed in the Soviet Union by Mikhail Kalashnikov.
AK-47