When the added velocity of a longer barrel needs to be preserved, but the desire for additional weight reduction remains, barrel fluting serves as an excellent solution to help shave away unwanted bulk. Criterion fluted AR-15 barrels are designed to ensure maximum concentricity and consistent dimensions throughout the full length of the bore. Eight flutes are machined around the circumference of the barrel to the front and rear of the gas port. Each flute is polished to smooth jagged edges while retaining a sharp appearance. Each 416R stainless steel barrel comes complete with an M4 barrel extension and a .223 Wylde chamber designed to accept both .223 Remington and 5.56 NATO cartri Mfg: Criterion Barrels Inc SPECS: Length - 18, or 20 inch. Profile - Fluted. Gas system - Rifle (18" & 20"). Chamber - 223 Wylde. Finish - Stainless Steel. Construction - 416R Stainless Steel. Hand Lapped. Includes barrel extension with M4 feedramps. Dimensions - .750" OD at th