Fair enough... thanks :redface:
Only reason I know a lot about this subject, is I spent a lot of time researching how to build a highly accurate AR. One of my future projects I want to build is a long range AR in .223.
Firing 75 grain, hollow point rounds (The largest possible round to fit in a clip), it is possible to be accurate at up to 800 yards or more. There are also people who hold records at a mile with them. This is rather an interesting concept of development on the guns. I really just want a .223 that will do around 500 to 600 yards.
Besides getting into ballistics in the round itself, there were major things that they recommended.
A heavy barrel was a must. Heavy barrels absorb the vibrations during firing better than a light barrel. When you fire, the propellant as it is burning, and sending the bullet down the bore, creates vibrations. Even if your gun, is somehow perfectly held in place by mechanical means, these vibrations will cause your grouping to be off. Hence why Heavy Barrels are preferred. This is where Cryo treating comes in as well. Cryo treating helps strengthen the barrel, allowing it to absorb even more vibrations.
Your upper "floats" on what you hold. You have 2 pins that connect your lower to your upper. Your buttstock and your pistol grip are part of the lower. This is where the majority of your control comes from when aiming. Your hand on the handguard helps steady it, but it is not what is taking the brunt of the force. If your upper is not tight to the lower, and there is a considerable amount of play, you need to find a way to help take up that slop. On most AR's, it's a simple 2 dollar purchase to "help" by purchasing a accuwedge. It fits under your rear takedown pin where the DIAS (Autosear) goes on the M16. It puts pressure on the upper receiver, forcing it upwards to tighten it. This helps get rid of your up and down play. However, in the case of the S&W I have, it literally has a noticeable amount of side to side play. The wedge can help a little with this, as it puts pressure upwards, and therefore, helps keep it from rocking a little, but the S&W is not DIAS cut, so a accuwedge does not fit.
One article I found, about accurizing a AR, the guy went to the hobby store and bought a very thin sheet of brass. He cut it to shape, bent it, made sure the hammer would travel through the hole he cut, and basically made an insert that went the full length of the lower. Not completely sure what the lower was he was using, but this was making a Match Rifle with off the shelf parts, instead of paying a premium of having a manufacture "match" him a set.
Free Float forgrip. You always want to take as much pressure off of the barrel as possible.
Proper barrel and bolt headspacing. This goes along with your rounds as well. Most everything else becomes preference of the shooter like trigger crap, spring tensions, loads, etc.
Anyways, I am just going on and on...
WarriorDriver, if I was to recommend a lower, just on pure beauty of how it is cleaned up and great fitting, I would go with a Defensive Edge SLR15 lower. They have a huge CY6 stamped on the side. It also comes with a Winter Trigger Guard, and a set screw to help put pressure on your disconnector to take up some trigger pull.
DPMS/Bushmaster/Remington - These are all going to be the relatively the same. All done on Common Machinery (All the same company).
Tactical Innovations out of Idaho, who manufactures for Spikes, Denny, and a handful of others.
SNS out of Snohomish - I looked these lowers over at the show, and they are cleaned up really well. Much better than a lot of the big shops. I know a couple people who are extremely happy with the quality and have built multiple AR's off of SNS lowers. Plus they are local! But unless you come down here to Gun Shows, it will most likely be hard to track one down right now.