Pistol caliber carbines such as 9mm, .40 S&W, .45 ACP, and 10mm are a blast to shoot but can be tough on AR-15 s internal components. Without a properly tuned blowback system, you run the risk of being overly destructive on internal lower parts. Running a blowback AR15 with a suppressor can further increase the risk for damage. Starting out your build with the KVP PCC Milspec kit is a great way to give your blowback system a fighting chance. Do yourself a favor and fine tune your setup for the softest shooting PCC possible. This kit is perfect for those who are building a Blowback Pistol Caliber Carbine rifle or SBR. This kit contains everything needed to install Mil-Spec diameter stocks from Magpul, BCM, MFT, Luth-AR, and many others. Product Features (1) 7075-T6 Aluminum Mil-Spec 6-pos Buffer Tube Matte Black Anodized (1) KVP Extra Power 17-4 SS PCC Spring (1) KVP 7.5oz SS Blowback Buffer (1) Carbine Stock Lock Ring-Castle Nut (1) Carbine stock end plate