This upgrade AR15 carbine action buffer spring is made for AR and M4 adjustable stock buffer tube to M4A1 Mil-Spec specifications. This AR 15 carbine buffer spring length is direct replacement for AR-15 carbine models and AR Variants. Buffer Spring is high quality and Made in the USA. This M4 AR-15 carbine buffer action spring fits all mil-spec and commercial carbine receiver extension buffer tube assemblies. By upgrading your worn AR-15 carbine action spring to a new one it will provides the extra power your AR-15 or M4 carbine rifle needs to cycle properly if your old one has weakened and failed. Limited lifetime warranty.