S&W 811000 M&P 15 Semi-Auto 223 Rem/5.56 NATO 16" 30+1 6 Pt Collapsible Stk Blk All feature 16-inch barrels with chrome lined bores, chambers, bolt carriers, and gas keys. The chamber specification is 5.56mm NATO dimension or 223 Remington, and the rifling twist is 1:9. The flash suppressor is the A2 military style. The upper and lower receivers are fabricated from 7075 T6 aluminum, manufactured in the U.S. by an independent contractor to Smith & Wesson's specifications. The machining, assembly, and final fit matching of the parts are done by hand in S&W's plant. The single stage trigger is factory set for a maximum break weight of seven pounds. All three versions feature standard sling swivels plus an additional side mount front sling swivel for two position sling option (swappable to left-side or right-side).