If I want to build an AR...do all the upppers come with the barrel extension already installed and to the correct depth?..all you have to get is a nice bolt and new barrel to get proper head spacing?

the extension is actually attached to the barrel not the upper and yes they are typically headspaced correctly if you use a new bolt.

I suggest that you do some more reading and maybe purchase a factory rifle first before attempting to build yourself.  IMO, it sounds like you haven't learned enough in 3 years on this site to begin your first build.

Geee...thanks for the great advise....

then why do they sell barrel extension wrenches..?Isnt the barrel extension the "claw" and feed ramps the bolt locks into when the round is chamber? I thought the barrel sits flush into the reciever up against the barrel extension  that is why everyone is saying that the headspace is determined by the bolt to bolt extension fit....
I guess I  am missing a something here ....

So i am assuming when you buy a new upper stripped reciever the barrel extension is already installed?

Quoted: Geee...thanks for the great advise.... then why do they sell barrel extension wrenches..?Isnt the barrel extension the "claw" and feed ramps the bolt locks into when the round is chamber? I thought the barrel sits flush into the reciever up against the barrel extension  that is why everyone is saying that the headspace is determined by the bolt to bolt extension fit.... I guess I  am missing a something here .... So i am assuming when you buy a new upper stripped reciever the barrel extension is already installed?

The barrel extension is on the BARREL> not the UPPER

Most, If not all barrels you buy have the extension put on from the factory/manufactor. If you wanted a BARE barrel you can get it and then you would hve to put the barrel extension on yourself and that is the one thing I will say needs to be done by a qualified gunsmith.

How is the barrel extension installed on barrel? Press fit? You can see I am new to AR.

If I want to build an AR...do all the upppers come with the barrel extension already installed and to the correct depth?..all you have to get is a nice bolt and new barrel to get proper head spacing?

Yes.


"why they sell barrel extension wrenches..."

For guys with a lathe and fixtures who are manufacturing barrels.

Changing an extension is not something for the average builder.  The time and effort involved is such that it is cheaper to buy another barrel.  You cannot pay a machinist for his time and costs to "change out a barrel extension" and not exceed the price of a new barrel.

Quoted: How is the barrel extension installed on barrel? Press fit? You can see I am new to AR.

It is threaded on and then pinned by the manufacturer or advanced hobbyist.

The barrel extension is very much like the front 2" of a bolt action rifle.  It contains the cartridge feed ramp and bolt locking surfaces.

As in a bolt action rifle, the bolt and the integral locking lug surfaces determine headspace.  The upper reciever in an AR just keeps everything together in a straight line and not much else.

EDIT:  Oh yeah, the barrel extension just slips right into the upper reciever.  There is a couple thou clearance, so the barrel will rattle around until you tighten up the barrel nut.

Just for context, here is a barrel extension picture showing both types:



Randall Rausch
www.ar15barrels.com