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Once again,apparently someone does not understand the mechanics of Stoner's AR design.
There are no locking surfaces or lugs in an AR upper receiver. Almost always,when you buy an AR barrel,it comes with a BARREL EXTENSION permanently attached to the threaded,chambered barrel.
The BARREL EXTENSION has the locking lug surfaces machined into it.The Barrel has the chamber machined into it,usually to a nominal depth,and usually to tolerances that will provide proper headspace when matched with a bolt.
For military weapons,the index pin pressed into the bushing is driven in to the point t stakes the barrel to bushing thread in place.The uninformed may see the AR barrel as one piece,but it is an assembly.
Its a good idea to buy a barrel with a matched bolt.The headspace gets checked to that barrel. The receivers and barrel nut might be 1000 miles away,but the headspace is fixed and checked.
The bolt locks into the barrel extension.The relationship between the breech face and and the chamber datum has not one thing to do with the upper receiver or the barrel nut.The actual rifle bolt NEVER TOUCHES THE UPPER RECEIVER,It only touches the barrel extension and the bolt carrier.
To those who insist the barrel nut has something to do with the AR headspace,no offense intended,but you just don't understand the AR.
That's not a problem with us. You might take a deep breath,shrug,and say "Oops!" Its no big deal. That's how we learn.
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