BCM PISTOL RECEIVER EXTENSION KITBCM PISTOL RECEIVER EXTENSION KIT W BUFFER SPRING HARDWARE FEATURES Pistol Receiver Extension Kit Buffer Tube For AR15 Pistols For your AR15, M16, M4 Pistol Lower Receiver. Pistol Receiver extension (buffer tube) machined from 7075T6 Hard Coat Anodized per Mil A 8625F, Type III, Class 2 1. 2" outside diameter. Will fit your ATF compliant SigTac SB15 type pistol stabilizing brace. Works with carbine buffer and action springs.