My most accurate AR sits on a Noveske "chainsaw" (blem) lower. Thought long and hard about selling it for 3-5x what I built it for in the panic, but just couldn't bring myself to gouge someone that much or give it up.
Lowers have no impact on accuracy unless so out of spec as to cause the BCG to do something goofy before the bullet has left the bore (bullet should be long gone by the time the bolt unlocks anyway). If you're shooting for tight groups, the forearm/rail is going to be well supported; which in turn will take up any of the slop in the pin-to-receiver(s) fit. Your optic is securely attached to the upper, so nothing between your glass and barrel ever changes.
Having said that, we tend to judge a gun by the non-critical features; engraving, bluing, figure in the wood, tool marks, polish, etc. Sloppy fit has come to be frowned upon in AR's, where too tight will get you killed in a gunfight if you need to clear a popped primer that's locking up your trigger and can't get the takedown pin(s) out. Then you say "Oh, but I only use blah blah blah ammo, and they're crimped in" - You can't say you'll never run out of ammo and won't use anything you can find if it came down to it.
Do the pins fit (takedown and trigger group), and does the mag drop free? Receiver extension cut square to the top shelf of the lower? If all is good, there's no functional difference from what generally sells for $50 all the way up, unless you're after the funky stuff like ambi and what not (which are cool).
My FN M16A2 in the army was looser than a $3 hooker (or so I've heard
), and it'd put rounds on target if I did my job with the booger hook.
I just put a $250 stock on a $40 lower, and that gun shoots single holes @50yds with a tactical scope.
