Once the manufacturing difficulties of non milled receivers had been overcome, a redesigned version designated the AKM (M for "modernized" or "upgraded"; in Russian: Автомат Калашникова Модернизированный [Avtomat Kalashnikova Modernizirovanniy]) was introduced in 1959.  This new model used a stamped sheet metal receiver and featured a slanted muzzle brake on the end of the barrel to compensate for muzzle rise under recoil. In addition, a hammer retarder was added to prevent the weapon from firing out of battery (without the bolt being fully closed), during rapid or fully automatic fire.  This is also sometimes referred to as a "cyclic rate reducer", or simply "rate reducer", as it also has the effect of reducing the number of rounds fired per minute during fully automatic fire. It was also roughly one-third lighter than the previous model.