Originally Posted by Phantom465
Thanks - I am building an AR from the ground up. Are there any other parts that I should be concerned about? What about the bolt / bolt carrier or upper receiver?
Upper receiver doesn't matter, so long as it made to spec (ie: caliber doesn't matter, just has to be an AR-15 upper receiver). So long as the bolt is made for .223/5.56 (no difference between them for the bolt), and is from a quality manufacturer, you'll be fine. I am partial to Bravo Company, Daniel Defense, and LMT bolts (in that order, usually - consequently, that seems to be the order of availability).
For reliability, the two most critical parts are the barrel and bolt carrier group. As long as you buy quality on those, you should be fine. Accuracy will vary between individual builds, so the only way to know how accurate YOUR rifle will be is to get out and shoot it.
Originally Posted by ked
i understand about the 5.56 or .223 wylde chamber, but can you be more specific about what exactly causes the excessive pressure?
A standard .223 chamber has a shorter leade than .223 Wylde or 5.56. Also, 5.56 cases have slightly smaller internal dimensions due to thicker case walls. Those two factors (tighter chamber and tighter internal case dimensions) contribute to higher chamber pressures. Bear in mind that this is all in GENERAL terms, as the exact dimensions can vary between production runs and manufacturers - sometimes dramatically.
Lucky gunner labs had a great write-up
on the two a while back, and it's worth reading.
Their conclusion was that, while shooting 5.56 from a .223 chamber isn't likely to turn your gun into a bomb (although it CAN happen in certain situations), it can potentially cause some issues - popped primers, or greater wear over time.