A firearm including a barrel having a chamber and an integrally formed upper receiver having a passageway, an accessory rail extending the complete length of the upper receiver, and a guidance feature extending along the passageway. The firearm also includes an operating rod having an anti-bounce mechanism, a bolt that is rotated counter-clockwise to lock against the chamber, a bolt carrier having a safety extension disposed below the bolt that prevents a hammer from striking a firing pin until the bolt is locked against the chamber, a lower receiver, a recoil spring assembly, and a fire control group. The bolt includes a polymer spring that biases a sliding extractor against the base of a cartridge. The sliding extractor is disposed at an angle ranging from thirty degrees to fifteen degrees on the bolt face to provide a low ejection angle from the firearm.