Ballistic Advantage BABL6MM001PQ Premium Series 6mm ARC 16" Threaded SPR Profile, Midlength with Low Pro Gas Block, Black QPQ 4150 Chrome Moly Vanadium Steel, Fits AR-15 $232.75
Springfield Armory XDM5001C Backstrap Sleeve made of Polymer with Black Finish & 1 Piece Design for 9mm Luger, 40 S&W Springfield XD-M Compact with #1 Backstrap $12.41