Includes an automatic bolt release that enables the shooter to simply pull back bolt slightly to the rear to release it. Also includes target grade hammer, hammer shims and hammer spring. Hammer is precision surface ground to provide a 2-1/2 lb trigger pull. Requires disassembly of the trigger assembly for installation. Notes: Some Ruger 10/22 models will require the use of two Ruger hammer bushings for proper installation (product 510559). 10/22's that already have separate hammer bushings will not need new ones as the factory ones can be re-used.