Well... unless something is really out of whack, I don't think the receiver or hand guard and for that matter the bolt carrier play that big a roll in this. Let me try to explain.
The barrel extension screwed into the barrel and the bolt lugs locking into the extension hold all the pressure and are the only sold lockup in the system. The bolt relies on gas rings to keep it lined up in the carrier, the upper receiver has enough slop in it to allow the carrier to run back and forth. Even a tight "bedded" barrel/receiver only keeps your sight plane straight.
Think of it as a bolt gun, you square the receiver to the barrel. In an AR this is the barrel extension into the barrel. The aluminum receiver will conform to the barrel extension, unless it's way off, it ain't gonna matter how square the receiver is.
Next you have a bolt guns bolt lugs lapped to get even support to line the case up. With an AR, the lugs lock into the extension to do the same thing. The pressure on the gas rings, the slop of the carrier inside the aluminum receiver play little to nothing on the way the bolt locks into the extension unless something is way out of whack.
So as long as the bolt settles squarely into the extension supporting the case squarely into the chamber, it's gonna shoot. At least that's my understanding of the system.
Please don't think I said it doesn't matter if anything else is square or not or read anything into this but if the bolt doesn't lock into the extension squarely and the chamber square to the extension, it'll never be right. I'm sure I explained it clear as mud.
I'm kind of following, except most guys say a freefloating handguard has a big impact on accuracy. Now, if you take my new to me Colt sporter target model into consideration, I'd say those guys are nuts. That rifle shoots pretty dang good. I don't really see any weird anomalies when shooting groups with it. No strange unexplained fliers. However, the little debacle I had with my Noveske NSR attachment screws contacting the barrel and greatly affecting accuracy was an eye opener. I'd have to say the uneven contact on the barrel could induce stress on the barrel, thus affecting accuracy. Maybe it changed the barrel harmonics just enough to make some shots really act up. The proof to the problem was when I ground down the screws and things went back to normal. It was weird. What it does remind me of is when you have too long of a screw in the front base of a bolt action and that screw is making contact with the barrel threads. This is a known issue and cause for inaccuracy. As with most platforms, its all the little things that add up and make a problem. Since we are talking how to get the most out of our AR rifles in regards to consistent accuracy, even the most minute issue should be addressed and not overlooked. Speaking of minutia, the guy I was talking to that owns an AR shop locally, said even the anti walk trigger pins makes a difference, as well as the captured recoil spring system. He says the more consistent you can keep things, the better accuracy you are going to get. That kind of makes sense as well..
