HDD MK46A1 PARA BARREL ASSEMBLY, 5.56 NATO. 41V50 MIL-SPEC HAMMER FORGED STEEL WITH 1in7 TWIST, CHROME LINED FOR LONGER MACHINE GUN OPERATION AND BARREL LIFE. FLUTED FOR BETTER HEAT DISPERSION AND LIGHTER WEIGHT. WE BUILD THESE WITH 1/2X28 MUZZLE THREADS FOR THE BEST RANGE OF MUZZLE DEVICES AND ACCESSORIES.  THIS BARREL IS 13.75" LONG AND WILL FIT THE  MK46, MK46A1, M249 WEAPONRY. DUE TO HAMMER FORGING, CHROME LINING AND FLUTING THESE BARRELS ARE SUPERIOR FOR SUSTAINED FIRE AND LONGER LIFE.