ARMY FOREIGN SCIENCE AND TECHNOLOGY CENTER CHARLOTTESVILLE VA
There are four classes of automatic weapons, classified according to the manner in which they make use of propellant gas energy in operating the automatic mechanism for reloading. The first class, featuring blow back bolts, uses recoil energy. The second class, consisting of gas operated weapons, uses propellant gas for reloading. The third class, characterized by blow forward barrel weapons, uses forward bolt energy. The fourth class is made up of assorted types in which reloading is based on several different methods. The report describes the mechanics of each class.
Trans. of unidentified Russian language article 7p 1972, by Derek Trombley.