For Silverback Airsoft SRS users, they will need to read this safety warning that the company issued... "Unlike traditional spring bolt action airsoft guns using the 90° sear system from Maruzen or the 45° sear system from Marui, the SRS is using a 'circular sear' system due to 'bullpup reasons' (and lack of space). The interface between the piston sear and the piston end is a circular surface.