The Rock River Arms 16 Inch CAR - CHROME-LINED - HBAR - RRA TRO Mid Rail Upper features a Rock River Arms 16 inch chrome moly vanadium, chrome-lined, HBAR barrel chambered in 5.56 NATO with a carbine length gas system, 1:9 twist and 1/2-28 threaded muzzle.  Built on an RRA flat top receiver with an RRA TRO Mid rail and an A2 flash hider.

These are assembled and test fired by PK Firearms. 

The Rock River Arms 16 Inch - MID - Stainless Steel - HBAR - RRA TRO Mid Rail Upper features a Rock River Arms 16 inch stainless steel, HBAR barrel, chambered in .223 Wylde, with a mid-length gas system, 1:8 twist and 1/2-28 threaded muzzle.  Built on an RRA flat top receiver with a RRA TRO Mid Rail and an A2 flash hider.

The Noveske 16 Inch Lightweight - Vltor VIS 2A-AK Midlength Extended Rail upper features a Noveske 16 inch lightweight, stainless steel barrel with a 1:7 twist, improved polygonal rifling, Noveske match Mod0 chamber, extended feed ramps, bead-blasted finish, mid-length gas system, pinned low-profile gas block, in a lightweight contour with a 1/2-28 threaded muzzle.  Built on a Vltor VIS 2A-AK midlength extended receiver / quad rail with M4 feed ramps, and an A2 flash hider.

These are assembled and test fired by PK Firearms.

The Rock River Arms 18 Inch - MID - Stainless Steel - Noveske NSR 16.7 Rail upper features a Rock River Arms 18 inch stainless steel, Heavy Match barrel, chambered in .223 Wylde with a 1:8 twist, midlength gas system, and a 1/2-28 threaded muzzle.  Built on an RRA flat top receiver with a Noveske NSR 16.7 rail, and an A2 flash hider.  Option available for Bead Blasted barrel finish.