The AR-15 magazine catch spring is a small coil spring that holds tension on the magazine catch in the lower receiver. It keeps the magazine catch engaged so the magazine locks securely in the mag well. Shooters press the mag release button against this spring to drop the magazine. The magazine catch spring installs as part of the lower parts kit and fits all mil-spec AR-15 lower receivers. Builders replace it to restore reliable magazine retention in any AR-15 build.
