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View Poll Results: Have you checked headspace on your built/re-barreld gun?
Yes 12 40.00%
No 18 60.00%
Voters: 30. You may not vote on this poll

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Old May 20, 2021, 09:28 PM   #1
Shadow9mm
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How many of you have checked your AR headspace?

Over the years I have replaced barrels on a couple ARs and built 1 up. I am looking to build another in the near future. I have never gauged the head space on any of them. I understood it was important however I justified not checking by telling myself that I had bought quality parts and it would be ok.

I watched a few vids recently and it really reinforced the importance of checking head space.
Quote:
tolerances found on a firearm are of more importance than headspace. Not only is headspace essential to rifle accuracy, but it is a major safety factor to consider when assembling a firearm. Improper headspace can cause case head separation, unsafe chamber pressure levels, or failure to function.
https://criterionbarrels.com/media/w...to%20function.

So I spent the money, $75, and bought a set of gauges.

I am happy to report that the guns passed without issue. However they could have just as easily failed. It is something you should know for sure on your rifle.

If you have built, re-barreled, or replaced a bolt on your AR, get it checked, whether you buy gauges, borrow gauges, or take it to a gunsmith.
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Old May 21, 2021, 12:31 AM   #2
HiBC
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I've checked headspace on every rifle I have built.IMO,its a gunsmith standard of quality work. Do it right or don't do it.

I received and returned a name brand, $375 cut rifled barrel for an AR that accepted the No-Go with the three bolts I had.

And yes,I initially ordered the barrel with matching bolt.Long story.Nothing would be served by telling it.
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Old May 21, 2021, 02:14 AM   #3
DaleA
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My fantasy gun club would have lots of stuff that is kind of pricey and not used very often that a person could check out, use and return and I think I'm adding a set of gauges to the list.

Note: there have been other threads about gun club equipment so I don't want to hijack this thread to get into that discussion here.
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Old May 21, 2021, 05:29 AM   #4
stagpanther
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I have gauges for all my AR builds, but have never had one that didn't pass (bolt gun builds it's virtually impossible to assemble one without good gauges). Far more likely IMO something else is going to indirectly cause a headspace issue over time. Things like failure to complete lock-up of bolt lugs to extension, barrel extension slightly out of clock, BCG wear and misalignment to upper's bore. So it becomes a question of how often do you check your headspace? Here I plead guilty, I often "set it and forget it" until the gun starts showing issues.

There is also the question of who's gauges you use--they are not all necessarily the same in tolerances. I generally stick with PTG or Manson. I once did a build using a barrel that came with gages--and one of the gages itself was out of compliance.
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Last edited by stagpanther; May 21, 2021 at 05:52 AM.
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Old May 21, 2021, 06:24 AM   #5
imashooter
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Never have. But I've never mated extensions to barrels. Other than that I've assembled several without incident. Used older bolts with new barrels, old barrels with new bolts, all that stuff. Never a problem.
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Old May 21, 2021, 09:41 AM   #6
ocharry
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when i decided to build an AR i sat down and started thinking about what tools i would need

the first 3 were a lapping bar and a reaction rod with a sail and a set of go-no go gauges

i like tools...lol ...the right tool for the job makes everything smooth sailing most of the time

just working on ladder loads for the AR i just finished and it functions like a clock, ejects at 3-3:30 and is showing really nice results with groups too

get the gauges....they are cheap in the long run

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Old May 21, 2021, 10:17 AM   #7
7.62 man
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I have checked many other guns I own but never my ARs.
From what I can tell if the bolt & the barrel are made right there shouldn't be any problem.
That's what the mil-spec part of the gun is, all the parts are supposed to work together no matter what gun they are in. So unless you have one that is worn out or has something wrong with it, it should work.
Buy quality parts & don't worry about it.
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Old May 21, 2021, 10:41 AM   #8
FrankenMauser
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I ran into issues with a BHW barrel (now 'Columbia River Arms' I believe). Part of solving that problem involved buying gauges. (And going through another bad barrel. But that's another story.)

Now that I have the tools, I use them.
It didn't change anything about the 'builds' that came afterward. But at least I know where things stand for those chambers.


*I did find a bolt that doesn't get along with a couple barrel extensions. But I didn't plan to use that bolt in those uppers, anyway. So, it didn't really matter.


Quote:
From what I can tell if the bolt & the barrel are made right there shouldn't be any problem.
How do you know they're made right? Calibrated eyeball?
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Old June 3, 2021, 11:49 AM   #9
Sweet Shooter
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Shadow9mm
Quote:
"However they could have just as easily failed. It is something you should know for sure on your rifle"
I think with the AR platform specifically things are a little different—because of the mil-spec aspect (when they are mil spec of course). Not diminishing the safety issue, but I have never had a problem as I have always bought mil-spec quality parts, or at least parts that observe the mil-spec data pack. It's important to note that some bolt makers make bolts for many brands and if you can find out who they are it adds confidence (AB Arms for example). But you're right, knowing is good. One thing I always check is what my FL dies do to a spent case in terms of shoulder bump, it will give some indication of whether you have a tight or more open chamber.
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Old June 3, 2021, 12:14 PM   #10
MarkCO
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I check them all the time, but then selling AR15 barrels at retail, I kind of need to QC the barrels.

That said, yes, I have found barrels that have excessive, and not enough headspace on ARs I have worked on.

When Melonite barrels first came out, I found several with excessive headspace.

I have yet to find a properly built barrel that was out of spec with a used or new bolt.
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Old June 3, 2021, 01:15 PM   #11
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I was rebarreling M16A1s for Uncle Sam in the 70s. There was always a headspace check. And, since all the parts used were from the Army supply system, it was assumed they were all "mil-spec". But we checked them, anyway. And yes, some parts did fail.

The GI solution to failing the headspace check was to try a different bolt, and keep trying different bolts until one passed. If none of the bolts in shop stock would pass, we then replaced the "new" barrel with another one, and trashed the one that failed, repeating the check process until we got a combination of parts that would pass.

Quote:
One thing I always check is what my FL dies do to a spent case in terms of shoulder bump, it will give some indication of whether you have a tight or more open chamber.
This is fine, but it doesn't tell you what you think it does. Yes, it does indicate if you chamber is tight, or "more open" but only in relationship to your sizer die, and how you have that die adjusted.

How do you determine if your sizer die has "tight" or "more open" specs?? Is it adjusted to give the maximum amount of case sizing possible? Or something else??

Everything has a range of tolerances, and they can stack up in different ways. A "generous" chamber (but still within spec) and an uber tight sizer die might lead you to suspect excessive headspace. The exact opposite could lead you to think headspace is insufficient. The headspace could be in spec in both those cases. OR, it might not be....

This is why we use gauges, made to a certified standard.
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Old June 3, 2021, 10:49 PM   #12
Bart B.
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Quote:
Originally Posted by 7.62 man View Post
I have checked many other guns I own but never my ARs.
From what I can tell if the bolt & the barrel are made right there shouldn't be any problem.
That's what the mil-spec part of the gun is, all the parts are supposed to work together no matter what gun they are in. So unless you have one that is worn out or has something wrong with it, it should work.
Buy quality parts & don't worry about it.
The flaw in that reasoning is the parts have tolerances that can add up to inoperable or unsafe situations.

Last edited by Bart B.; June 3, 2021 at 10:58 PM.
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Old June 3, 2021, 11:37 PM   #13
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Quote:
From what I can tell if the bolt & the barrel are made right there shouldn't be any problem.
When your parts are made right, there isn't any problem, but, other than blind trust, how do you ensure that?

Back during WWII, when we had nearly every shop in the country turning out some kind of part(s) for military use we also had (created and trained) legions of govt inspectors, to ensure that what was being made to "mil spec" actually WAS made to the spec, checked and passed before it went into the military supply system. Gun parts, were just ONE of the thousands of things that had to pass govt inspection or they didn't get bought.

There is no such thing today on the civilian market. All we have to go on is the word of the maker, and some of them are less than fully diligent about their QA/QC.

I get a kick out of ads that claim "milspec" but "might require some fitting"....
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Old June 4, 2021, 06:54 AM   #14
jetinteriorguy
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Quote:
Originally Posted by 44 AMP View Post
I was rebarreling M16A1s for Uncle Sam in the 70s. There was always a headspace check. And, since all the parts used were from the Army supply system, it was assumed they were all "mil-spec". But we checked them, anyway. And yes, some parts did fail.

The GI solution to failing the headspace check was to try a different bolt, and keep trying different bolts until one passed. If none of the bolts in shop stock would pass, we then replaced the "new" barrel with another one, and trashed the one that failed, repeating the check process until we got a combination of parts that would pass.



This is fine, but it doesn't tell you what you think it does. Yes, it does indicate if you chamber is tight, or "more open" but only in relationship to your sizer die, and how you have that die adjusted.

How do you determine if your sizer die has "tight" or "more open" specs?? Is it adjusted to give the maximum amount of case sizing possible? Or something else??

Everything has a range of tolerances, and they can stack up in different ways. A "generous" chamber (but still within spec) and an uber tight sizer die might lead you to suspect excessive headspace. The exact opposite could lead you to think headspace is insufficient. The headspace could be in spec in both those cases. OR, it might not be....

This is why we use gauges, made to a certified standard.
Thanks for this, it actually answers my question in my post on my 6.5x55 Swedish Mauser brass in the thread that I started.
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Old June 10, 2021, 10:22 AM   #15
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@44 AMP:
Quote:
"How do you determine if your sizer die has "tight" or "more open" specs?? Is it adjusted to give the maximum amount of case sizing possible? Or something else??"
I have always let the press cam over (within reason), and I measure and compare new or unknown dies, and the resulting brass with micrometers. Not saying it's a perfect method but in a pinch it will 99.99% work. I'd also hazard a guess, and say that tolerances in good die manufacturing are as good as gauges. Gauges can add to tolerance stacking too.
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