[mrmeyer]

If the AR-15 platform in 5.56x45mm is what you're considering, determine which barrel length (16 vs 20 or 20+) and twist rate 1:7 or 1:9 will be best for the bullet weight (55,62,69,77 etc) you plan on using as well as the distance at which you intend to shoot/zero in. There are govt. profile barrels, HBARs, and stainless steel as well as free floating.

You can find plenty of useful info at AR15.com comparing brands, features, and parts if you choose to build your own. Good luck.

[gundog]

...and twist rate 1:7 or 1:9 will be best for the bullet weight (55,62,69,77 etc)

I see a lot about the twist rate in terms of accuracy....sure, a stable bullet will squeeze out the most a system is capable of, accuracy-wise, but when you're talking about a 16 in. barrel, would not there be some advantage in having a round that is just waiting for an excuse to tumble like crazy? Never heard of any ballistic gelatin tests to confirm, but it seems the terminal ballistics of, say a 1:9 twist rate and a 62 gr. or heavier bullet would be pretty ferocious.