Had to return. defective from factory. verified by gunsmith - Yankee Hill Machine Specter XL Black Diamond Carbine Complete Upper 5.56mm NATO 16 Inch Barrel 17 Inch Twist Rate YHM-7820-7

I purchased this upper to complete a gun I planned to use for 3-gun competition and sport shooting. There were immediate issues that could not be remedied and the gun was sent to a professional gun smith for evaluation. The gunsmith determined that the barrel included in this upper was defective. The best that the gun could shoot regardless of scope and shooting rests is a 6 inch group at 50 yards. The tests were conducted using factory XM193 military grade ammunition. This was the biggest disappointment in any firearm purchase I have ever made.