An error in an early article covering the AR-15 described the system as a "direct impingement" system. This long standing error is based on the fact that a true direct impingement system also moves propellant gasses from the barrel into the face of the carrier. Unlike pressurizing a piston cylinder in the bolt carrier, the gas of the direct impingement system simply passes into a shallow depression in the bolt carrier and actually blows the carrier to the rear. 