This upper offers a 1:8 RH military twist rate, chrome lined barrel. It is also made of 41V50 chrome-moly steel, barrel is dimpled for gas block. We recommend using locktite on the gas block screws before final assembly. Our uppers have had extra work put into them. We deburr the feed-ramps and polish the chamber for the highest reliability. We use MIL-SPEC barrels for these. We use nothing but mil-spec uppers, they do have the M-4 ramped barrel and receiver. At a length of 16" it's pretty darn short also it has a 5.56 NATO chamber. We recommend a 62gr bullet for best accuracy.