There's zero argument. An AR15 lower affects accuracy by zero percent. It can affect your ABILITY to shoot accurately(read: trigger group, grip-to-shooter fitment, etc), but has no impact on the rifle's accuracy.
Everything--and I mean everything--that makes or breaks an AR's accuracy is in the upper. Bolt, chamber, barrel...yep, all there.
That all being said, I appreciate the "anti slop" device in my Sig M400 just for what it is, making my carbine feel more solid.
