AR10 A4 (flattop) upper. However this is the 20" heavy stainless barrel, more like a T than a standard. Not catalogued or stocked any more. Unfired, with bolt and carrier. Muzzle brake is the one which is ground smooth. Unles I'm reading it wrong, some comments I've seen indicate one needs only find the pin head by a discoloration on the brake (I think I can see it), grind it there and spin off. Can't vouch for the procedure, but that's what I have seen on AR10 forums. $700. shipped.
Will add cash in trade toward a .300 RSUM upper.