I see that most manufacturers sell uppers either with or without a bolt assembly.  As far as headspace is concerned, can I swap an upper and use the bolt in my orginal rifle?  If I can, then that would mean that head space is done without a bolt.  In another words to keep proper headpsace, the bolt and barrel do not need to be matched like most other semi auto designs and bolt action rifles.  Am I right?  This seems like a simple question, but I can't find and answer to it anywhere?

Also, when the AWB sunset occured, I had my post ban barrel threaded and A2 FS put on it.  To do so, I presume the shop had to remove the barrel from the upper to turn it to thread it.  When they put the barrel back on, they did not have my bolt.  (I just gave the shop my upper with no bolt or lower.)  Would that matter?  Could the headspce be correct if the shop did not have my bolt?  How could they check headspace without the bolt?      HELP!!!          

     

Oh boy. here we go again.

Headspace? I thought that was the distance between your lap and the steering wheel.

Good one! I should explain my previous post.  Just read the headspace thread in build it yourself and you'll understand why i said " Oh boy, here we go again.

Quoted: Oh boy. here we go again.

+1

Quoted: Headspace? I thought that was the distance between your lap and the steering wheel.

Nope, I thought it was the empty space between one's ears?

I know what headspace is and how to measure it.  The sticky in "Build it yourself" does not really answer my question other than what headspace is and saying that the barrels should be in specc as should the bolts.  That's the case with any rifle barrel.

I am assuming now that the diference between an AR-15 barrel and say a bolt action barrel is that the bolt in a bolt action locks into the receiver and the bolt on an AR-15 locks into the actual barrel.  Is that correct?        

Quoted: I know what headspace is and how to measure it.  The sticky in "Build it yourself" does not really answer my question other than what headspace is and saying that the barrels should be in specc as should the bolts.  That's the case with any rifle barrel. I am assuming now that the diference between an AR-15 barrel and say a bolt action barrel is that the bolt in a bolt action locks into the receiver and the bolt on an AR-15 locks into the actual barrel.  Is that correct?

The bolt locks into the barrel extension...

ETA: Below is a thread that will probably really confuse you...

ar15.com/forums/topic.html?b=3&f=4&t=263345

Actually though, if you can sort out the bull, it should be helpful...

I went through the HS process recently troubleshooting a malfunctioning .223 chambered DPMS.  Here's the short version of what I learned after playing with GO and NOGO gauges and comparing several different bolts (some new, some old, all different makers) and different barrels:

1) Of course, no adjustment --- a spec bolt will have headspace within spec when mated to a spec barrel (both being new).
2) There are ever-so-slight variations between makers, so if you tried enough combinations you could find a setup that would result in slightly larger or slightly tighter headspace.
3) The amount of use will gradually make the headspace dimension looser on both bolts and barrels.  Really well-used bolts should not be used for a new build to go another several thousand rounds, as during that time the HS might become too loose.
4) When building a rifle, always check the HS as a cautionary measure (i.e. every AR enthusiast should have a Field Gauge at minimum.  5.56 Field Gauges are available from Fulton Armory.

Last time I worried about headspace was firing a Ma Deuce about 20 years ago in the army.

The bolt does not need to be matched up as long as both the bolt and barrel assy are in spec.  The barrel's headspace is set at the factory by the barrel extension. The bolt is manufactured to a spec that provides proper headspace with an in-spec barrel assy. A "matched bolt" like those that CLE provides are just bolts that headspaced to the minimum proper headspace.  Wear and minute variations in manufacturing will cause the headspace to vary but nothing to worry about.  It would take bad manufacturing or really excessive wear for the AR to be out of headspace.

I got it now.  Thank you all .