Guess this guy has an Hbar but did they make steel lowers?  http://www.armslist.com/posts/6555115/denver-colorado-rifles-for-sale-trade--1980s-preban-ar15

Once upon a time, more like the late 90's - 00's DPMS made stainless steel lowers but I think they were sold only as stripped lowers and not as complete lowers or rifles.  

But his ad says "Colt" as the manufacturer.  

Colt did many different things with it's parts availablity but a steel receiver was NEVER an option with them.  

I don't know what he has but it's 100% not a Colt factory rifle.

There is also a good chance that the guy just can't the difference between aluminum and steel.

I think it has some kind of weird fixed flash hider. I've run across one that looks like that at a gunshow before.

Thanks for the answers