In high power matches, all service rifles are equiped with a free-float tube under the handquard. The sling is attached to the FF tube and not the barrel. Sling tension and it corresponding flex is isolated to the FF tube and not the barrel. Since the barrel is isolated from the sling tension, sight alignment is consistent from shot to shot. If you are going to be shooting optics mounted on the upper receiver, iron sight placement is not an issue. If you are shooting iron sights, the front sight must be attached to the barrel and not the FF tube. Hope this helps. Art
