The embodiments described herein relate generally to a sleeve piston for operating the bolt carrier of a firearm. The sleeve piston can comprise a monolithic sleeve piston or it can comprise two or more sleeve-piston parts, thereby evenly distributing the reciprocating mass of an auto-loading firearm about its barrel, minimizing muzzle rise. The sleeve piston can further be coupled to the bolt carrier by two or more operating rods, thereby reducing the tipping force or off-axis torque experienced by the bolt carrier during firearm operation. The sleeve piston can also reciprocate in a sleeve gas block coupled to a barrel, thereby helping to transfer heat away from the barrel. The sleeve piston embodiments of the present invention provide a balanced and compact operating mechanism that is ideally suited for rifles, carbines, and personal-defense weapons.