Information can be found in these places:
http://www.hdrifles.co/warehouse/index. ... -rail.html
https://www.primaryarms.com/Head-Down-P ... hdpr13.htm
Ar-15 discussion on the rail:
http://www.ar15.com/forums/t_3_4/627366 ... ystem.html
Looks exactly like this.
This was designed, and made by Seekins Precision for Head Down. Brand new, in the box. I ordered a 15" and a 13" to decide which one I liked better. I went with the 15". The only marks on this rail are around inside diameter where it slide over the barrel nut when test fitting, the barrel nut has not been installed on a rifle. The rail has two anti-rotation tabs that hug the top of the mil-spec upper. This is a really nice piece that has a decent amount of features for the price.
Comes in original packaging, barrel nut, and all necessary hardware.
$125, no shipping.
15" rail installed on my rifle for some idea of what it looks like (crap cell pic)
Would consider a trade for an AR15 muzzle device, specifically the Lantac Dragon.