An alternative to direct impingement rifles, a gas piston operating system uses redirected gas from a fired round to drive a metal rod, or “piston,” rearward, impacting the bolt and carrier which extracts the spent casing. Many believe gas piston semi-automatic rifles are more reliable and less maintenance-intensive than direct impingement ones. Gas piston AR-style rifles often feature adjustable gas blocks that are placed near the end of the barrel which allows shooters to tailor the amount of gas used to drive the piston rearward. This is particularly useful in cases where the shooter is using a suppressor, since less gas from a fired round exits the barrel, creating a situation where the bolt and carrier are subjected to excessive force.