The Sig Sauer Sig 556 DMR is a semi-automatic tactical carbine chambered in 5.56 NATO. The DMR has the most advanced features of all the 556s in the series and costs about $600 more than the standard.
Unlike the standard 556, the DMR is gas operated instead of gas piston operated, so the propellant gases flow through a tube aimed at a tube in the bolt. The gas pushes the bolt to cycle the action.
Features on the DMR include a 21″ military grade, cold hammer forged, heavy barrel. Cold hammer forging means a machine carefully cut grooves in the bore. The process leave the grooves very durable. It has a target crown that helps maintain barrel harmonics, so when a round is fired vibrations in the barrel won’t throw off the projectile’s trajectory. The handguards are vented and made of polymer as opposed to plastic. It has Picatinny rails running along the top, bottom and sides of the handguards for easy mounting of optics or accessories. And it has an ambidextrous safety, a single-stage match trigger to set off the action with a short pull, and a bipod.