Originally Posted By UndrGrndPrdcts:
So between 10-12 inches, and does it have to be free float? I'm mainly not sure about how it attaches.
It needs to be a free floated rail if you want the gas block covered. Non-free float rails need a handgaurd cap behind the gas block to retain them, so they can't really extend over the block.
I would recommend a 10 or 12" Troy MRF. They use the factory barrel nut, and if you don't mind cutting off the delta ring, you can install it without removing the barrel nut at all.