The San Tan Tactical Enhanced Mil-Spec AR-15 Bolt Carrier Group was designed for shooters who demand superior performance weapon components in the heart of their firearm. Carrier Assembly: The flared rear of the enhanced bolt carrier is designed to reduce carrier tilt during recoil and increase reliability by strategically relocating key bearing surfaces. Made from Case-hardened 8620 steel. The STT enhanced carrier has sand cuts to improve reliability in heavily fouled guns. The increase in mass ensures proper gas pressure and increases dwell time, thus improving extraction while shooting suppressed or short-barreled rifles (SBRs). Bolt Assembly: The Bolt is a "true" Mil-Spec dimension. The external surfaces are CNC ground after heat treatment for a precision fit. The bolts are held to the highest possible tolerances. The "trumpet" area behind the gas rings, where carbon collects, is precision CNC Ground after heat treatment, to ensure as smooth of an area as possible, easing clean ...