I own an AR-15. This is not uncommon. It uses the 9 inch midlength gas system. I prefer that length for a 16 inch barrel, unfortunately very few AR parts makers tool for it. Lots of them only do rifle and carbine length. If I wanted to free float my barrel, I could go to Rock River for a tube or YHM for rails or cut down a rifle length part or spend a lot of money. I even asked several parts shops at small arms conventions I attended in May whether they were planning on supporting midlength. Several hemmed and hawed, but surprisingly it was the guy at the UTG/CAA booth that felt my pain.
UTG now has an aluminum midlength free-float rail. Not sure I want UTG parts on my gun, but I don't think I mind them putting some downward pressure on the market. More importantly Hogue is now making midlength free float tubes for less than $50. Now that's something I might pick up and put on my gun.