Quoted:
My rifle isn't a bull barrel, it's a normal military grade barrel. I've looked and Daniel Defense doesn't have an option, nor does MI. All their options are not meant for piston rifles. I want a quad railed handguard, I guess I'll just have to stick to a normal 7" carbine rail, I just wanted the extended handguard for a longer grip.
Edit:
Had some extra time today to do some looking around, a friend of mine recommended ERGO brand, so I looked into them.
http://ergogrips.net/products/rails/overshoot-rail.html
Says it is piston compatible, I have emailed them to see if it is certain ones, or universal. Cheaperthandirt has it for $209, so it falls perfectly in my price range.
Oh? I only assumed it was a bull barrel 'cause the rifle in the link you included, is. Not the same rifle?
Anyway, glad you found something. I found this from Samson @ MI: http://www.midwayusa.com/product/2852128132/samson-evolution-series-customizable-free-float-handguard-ar-15-aluminum-matte?cm_vc=subv12696411402
They've got a couple of lengths with the extension / cutout. Not sure if the ID will give enough clearance @ 1.56"
If you don't mind, let me know if you find out the inside diameter of the ergo.
Here's a question: with so many different types, lengths and heights of operating systems and blocks on ARs now, why isn't anyone making a customizable, truly modular rail system?