I am building my first AR and would like to build a carbine that is robust, yet very accurate. I would eventually like to mount an IOR 4X M2 scope on the rifle. I currently have a 15" RRA barrel (chrome lined) with a permanently attached A2 flash hider on it.

How much more accuracy could be expected by mounting a free float tube (i.e., MI 2 piece free float) compared to a standard 2 piece non-free float rail?

Thank you for your advice!

more than one could possible post in this single reply

If you mount optics or such on a non-free-float tube, it's my understanding that they won't hold a good zero.

If you're mounting your sights on your receiver, then the accuracy gains are probably minimal, if noticeable at all, depending on the ammunition you use.