Ruger SR-556/6.8 Posted August 26, 2010 in AR-15, Rifles by Steve Johnson with 29 CommentsTags: ar, ar-15, rifle, rifles, ruger Ruger AR-15, the SR-556, is now available chambered in 6.8mm SPC. The SR-556/6.8 has .850 heavy contour barrel with a 1:10 twist. It comes packaged with a 5 round and a 25 round magazine. The MSRP is $1995.00. Win the new Springfield Armory XD-9 Mod.2 TFB's first ever gun giveaway.