A barrel chambered for 5.56 will also reliably fire .223. If you push a 5.56 round ito a .223 barrel, the primer may pop out of the casing and fall into the trigger mechanism. Bad news. A 5.56 barrel just doesn't care what you feed it. Chrome lining is irrelevant for modern ammunition for a semi auto. Go for chrome moly or stainless for accuracy. 1:9 twist for most bullets commonly available.
A "production model" costs more than a "build it yourself" and the results are essentially identical.
If a production of factory built model has the name "Colt" on it and you leave it unfired in it's original box, it will likely do better than most stocks have.
A do it yourself is definitely the way to play, you can build precisely what you want and most people wind up saving $200+. Building them is as easy as assembling a lego toy. Here's the info
http://www.mapartsinc.com/anything.asp
You would buy a
stripped lower receiver. $80 to $150. Just get one that is milled and forged. Then go buy yourself an AR15 Kit. They include all the pieces that you snap into the lower receiver, the buttstock, as well as the fully assembled upper receiver and barrel assy, which you just snap on top.
Essentialy, all lower receiver parts kits are the same
if they are made to the same usgi milspec that the government buys. M&A Parts is reliable in this regard and a great value. Remeber- no one is getting usgi milspec parts because that means that they would have to have been recvd by the government first. But there are parts being sold that are made to those specs.
They can sell you whatever buttstock, handguard, pistol grip, barrel configuration, flat top or carry handle that you might want- or just get a standardized kit. Again- assembling one is easy breezy- they even have the military manual with step by step directions for $5. Or- read it off the internet. The hard part, assembling the upper (receiver, barrel, handguard, bolt carrier assembly)- that has already been done.
Build it yourself, brother. Call
www.mapartsinc.com and talk to Andy. He knows the ar15 better than most.