Gonna buy a 20 or 24" AR and both of the guns I am looking at do not have rails that you can affix a bi-pod or front folding sight. Was thinking some bolt on 3" quad rail that goes over the gas block would work. Both of the weapons I am interested in have free float carbon rails and are open at the muzzle end of the barrel. Any suggestions or should I get the quad rail gas block dilly?