Sons of Liberty Gun Works believes in Quality Mil-Spec or better parts. They believe there is no substitute for quality and that your gun should be built right the first time, ready for hard use right out of the box. This is why they use the highest quality 7075-T6 Aluminum, with a Hardcoat Type III and R5 Bright Dip finish on all of their M4 Upper Receivers to achieve the best tolerances.