Kratos Design Group A5 Receiver Extension Black. This receiver extension is slightly longer than the traditional M4 receiver extension to utilize rifle length springs and A5 buffers and is designed to work with Mil-Spec dimensioned M4/AR-15 type collapsible stocks. For AR15/M16 applications it must use Vltor A5 or A5 compatible buffers and rifle length recoil springs Kratos Design Group reccomends the Sprinco Green Spring for most applications. This receiver extension tube can also can be utilized as a replacement receiver extension for the AR-10 rifle. Dialing in the perfect length of pull is easy with eight adjustable stock positions. The Kratos Design Group buffer tube is made of impact-extruded 7075 Aluminum and is made to withstand rigorous use. The finish is a Type III Class 2 hardcoat anodize. Specifications for Kratos Design Group A5 Receiver Extension: Manufacturer: Kratos Design Group Finish: Hardcoat anodize Fabric/Material: 7075 Aluminum Gun Make: AR Platform Gun Model: AR-10 M4 AR-15 Gun Type: Rifle Package Contents: Kratos Design Group A5 Receiver Extension What firearm models does the manufacturer say Kratos Design Group A5 Receiver Extension is compatible with? The manufacturer says that Kratos Design Group A5 Receiver Extension is compatible with AR-15 M4 AR-10Kratos Design Group RE-A5-BLK-KDG: A5 Receiver Extension Black