My buddy's RRA has an extremely tight fit between the upper and lower. Of all the other AR's I've handled, his has significantly less play. Is this typical of RRA, or did he just end up with a nicely matched set? Which manufacturer make uppers and lowers with the tightest fit? While a little play between the receivers doesn't matter as far as funcationality is concerned, I do find it irritating if it's significant. I'm getting ready to order the receivers for a new build, and while I typically go with Bushmaster, I am now looking at RRA due to the impressive fit on my friend's gun.

Thanks for your input.

MEGA machine receivers tend to have a good history of almost zero play/movement once mated together. My Mega to Mega build has zero movement as does my Mega lower with Leitner-Wise upper.

RRA's lowers are typically machined to be tight around the take down pins, especially the rear one.  

IMO, this is a good thing, as when you put the first 100-200 rounds through it the fit between the upper and lower becomes perfect, and that is not an understatement.  

It is almost as if they loosen together to the point that you would be hard pressed to find an upper or lower that fits as good as the one on it now.