An advanced gas piston operating system for Armalite Rifle (AR) and Armalite Rifle variants. The advanced gas piston system may include a barrel having a gas port formed through the barrel wall, a gas block assembly, a gas piston assembly, and upper receiver assembly, a sending block, rack and gear assembly, and a bolt carrier assembly with an attached rack. In such a system, a portion of the combustion gases from a fired projectile travel through a gas port in the barrel into a gas block assembly which drives a piston forward which compresses a main spring on an attached rod. The opposite end of the rod is attached to a sending block rack and gear assembly with the gear rotatably engaged with the teeth of another rack that is attached to the bolt carrier assembly. As the gas piston assembly moves forward, the bolt carrier assembly moves rearward until the main spring is fully compressed. Decompression of the main spring returns bolt carrier assembly forward loading the next round into the chamber.