A buttstock shoulder stabilizer includes a locator ball having a radially-projecting threaded cylindrical stud that screws into the sling mount of the buttstock endplate of assault rifles, and a socket assembly that mounts on a soldiers flak jacket near his shoulder. The ball can be machined from a structural metal or made of thermoplastic injection molded about the cylindrical stud. The socket assembly has an oblong horizontally-disposed socket connected to a lower approach ramp. A wall surrounds upper and side portions of the socket and the side edges of the approach ramp. When the soldier brings his weapon to firing position, the ball slides up the access ramp an into the oblong socket. The socket assembly is preferably injection molded from a tough structural thermoplastic resin. The socket assembly is provided with slots which enable it to be strapped to a soldiers flak jacket near his shoulder.