The short stroke gas piston operating system is common on modern rifles. It is defined as a gas piston which travels less than the distance of the bolt carrier (and is thus by definition not connected to the bolt carrier). This is in contrast to the long-stroke gas piston, which travels the full length of bolt carrier movement. The short stroke gas piston system was first made popular in the Soviet SVT-38/40 rifles, and was used in the Armalite AR-18, which formed the basis for many modern semiautomatic rifles.