AR15 checking headspaces?

[fzd]

straight question: do we really need to check headspace if the upper receiver, barrel and bcg are the same brand? I recently built two ar15s, all using Aero Precision parts. It has good reputation but just wondering if any one experience out of specs parts?

Thank you.

 

[johntheplinker]

Always a good idea to check any time you build new or replace a bolt or barrel on anything. You'll probably be o.k. but when you aren't, well...

 

[indyjohn]

I do not own or have access to a headspace gauge for an AR. I have numerous AR builds that have successfully fired hundreds of rounds without failure.

That statement says that I have put my trust in the manufacturers that produced the components have ensured that the pieces I have purchased to assemble those builds are in spec. Some think that is adequate, some do not. The AR barrel / receiver mating design inherently does not have the same challenge as the screw the barrel into the receiver design.

This is not to say AR building is foolproof, but certainly less of a risk than is with older designs.

 

[easy]

AR design is headspaced on the receiver extension. Nothing to do with upper receiver. Bolt and barrel assy.

 

[JEBland]

AR design is headspaced on the receiver extension. Nothing to do with upper receiver. Bolt and barrel assy.

How so? I'm not exactly sure what you're saying here, so this is a slightly tedious reply.

To avoid any terminology confusion, when I think of a receiver extension it's the lower receiver extension that holds the buffer weight and spring, and the barrel extension is the part of the barrel that comes out and into the upper receiver. The bolt's teeth go in then rotate to lock the bolt into firing position forming the firing chamber.

Naively, if the bolt is locked into the barrel (inside the barrel extension), when the gun is in battery, the bolt and the barrel form a closed system minus the bore for the bullet to, well, leave. As far as I can tell, when people talk about headspacing an AR, they're measuring the chamber formed by the bolt and barrel since that's what forms the chamber. So the headspace is a function of both a particular barrel and a particular bolt.

Granted, the buffer system and receiver extension needs to have the right properties to time the action and put the gun into battery, but I fail to see what that has to do with headspacing.




To the OP, @fzd ,
I did headspace my 300 BO build, and probably will continue to headspace just as a precaution. But many people have succeeded with the "it probably won't blow up" approach. Not my style.

 

[NyleRN]

To the OP, @fzd ,
I did headspace my 300 BO build, and probably will continue to headspace just as a precaution. But many people have succeeded with the "it probably won't blow up" approach. Not my style.

You actually headspaced your 300 blk or did you check it?

 

[JEBland]

You actually headspaced your 300 blk or did you check it?

Fair question. I checked the headspace of it using Go/No-Go gauges. I don't have equipment or expertise to adjust the headspace at home.

 

[BigRed3588]

straight question: do we really need to check headspace if the upper receiver, barrel and bcg are the same brand? I recently built two ar15s, all using Aero Precision parts. It has good reputation but just wondering if any one experience out of specs parts?

Thank you.

I’ve never received anything out of spec but have read reviews from people claiming they did. Pretty sure I’ve seen a couple YouTube videos about it as well.

Even if I hadn’t seen the reviews/vids, I’d still check it. My father in law has 30+ years experience as a machinist for various firearms manufacturers and I’ve heard some stories.