Besides a nice barrel, freefloat,trigger,,,what else can I do during a build to get the best accuracy and reliability?...

a good bolt/carrier




a good scope

You've got the components figured out. Now put them together correctly. Make sure the barrel is tight in the upper, and don't screw up the crown of the barrel.

As much as any of these thing if you want an accurate shooter use good quality ammo. FMJ and surplus is great for milk jugs, clay pigeon at 50 meters, dirt clods, etc. but to really find out how well your gun (and you) shoot (will it shoot under 1 MOA?) try some name brand ammo loaded with HP or SP bullets.

Then shoot off a bench with a good rest, sand bags...you know the drill...just like you were carefully sighting any other gun.

Why would the bolt make a difference - I'm curious.
Thanks

Quoted: Why would the bold make a difference - I'm curious. Thanks

I'm going to guess you meant to type bolt,

In regards to building up a sub MOA rifle, the bolt is part of the works that dictates the head space on the combo.  What should have been typed was that the bolt should be fitted to the barrel, and it and the barrel should be ream (as part of the lock up) to match spec's as a unit.

Corrected - bolt.
I have seen numerpus bolt carriers and all the bolts seem the same (except new LMT).
I suspect as you state, a better lock up would be better. Can they be matched to a barrel extension? How is that done?
I would much more would be gained in the land etc....

Quoted: Why would the bolt make a difference - I'm curious. Thanks

I think for a quality precision AR they match the bolt to the barrel at the factory/custom shop.

Quoted: . Cat they be matched to a barrel extension? How is that done?

First off, proof read your post before hitting the submit button (or at least do what I do and come back and edit it for mistakes.

As for a custom barrel/bolt, the bolt is lapped into the barrel extension (lugs to lugs).  This mates the two parts, then once the two are mated, the barrel chamber is final cut/finished reamed for the head space determined by the lapped in bolt.

Sorry for the typo...
Makes a lot of sense. I always thought the beauty of the AR (as compared to the M1, M14..) was that this was not required and assumed  the same for higher precision on an AR. I still feel the chambering is more critical (and the right ammo).
The last target uppers I had built (with Kreiger barrels) did not have this option - I had a choice of carriers though and selected a standard carrier and bolt.
Can you tell me which gunsmiths can do this?
Thanks

www.compasslake.com/

From the parts page (bottom of the site)

*2) To have the most accurate system CLE recommends a new, minimum head spaced bolt with each new barrel.  If you don't want  to go to this expense, we will ensure that you old bolt meets mil. spec head space requirements.