AR15.Com Archives
 Headspace Gauge Question
GHPorter  [Team Member]
10/9/2010 2:40:58 AM EST
Firstly, I know that "you shouldn't need to check headspace on an AR barrel and bolt." This of course assumes that your new barrel and new bolt are actually made to be within specs-which is apparently a problem in some cases.

My question is about which gauges to consider purchasing. Since every single headspace gauge I've ever seen is exclusively built to measure JUST the headspace, leaving the neck, freebore and leade completely out of the picture, is there any reason to go only with .223 Remington gauges or only with 5.56mm gauges? Is the SAAMI standard for headspace measurably different from the NATO standard? Is there one specific brand of gauges that is actually superior to others? Finally, is there a reliable, quality set of gauges that is made with an extractor cutout so that headspace testing could be done without disassembling the bolt first?

Thanks!
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WI57  [Team Member]
10/9/2010 4:57:14 AM EST
There is a military headspace gage that measures maximum headspace. They can be found on surplus websites for $50 or so.
They are shaped so you do not have to take the extractor out.
Otherwise a set from brownells would work fine.
Brownells also sells a throat erosion gage that would be nice to have if you want to follow the wear in your barrels throat.

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CAC01  [Team Member]
10/9/2010 5:55:53 AM EST
Originally Posted By GHPorter:
Firstly, I know that "you shouldn't need to check headspace on an AR barrel and bolt." This of course assumes that your new barrel and new bolt are actually made to be within specs-which is apparently a problem in some cases.

My question is about which gauges to consider purchasing. Since every single headspace gauge I've ever seen is exclusively built to measure JUST the headspace, leaving the neck, freebore and leade completely out of the picture, is there any reason to go only with .223 Remington gauges or only with 5.56mm gauges? Is the SAAMI standard for headspace measurably different from the NATO standard? Is there one specific brand of gauges that is actually superior to others? Finally, is there a reliable, quality set of gauges that is made with an extractor cutout so that headspace testing could be done without disassembling the bolt first?

Thanks!


All good questions. If they could be answered to your satisfaction, what would you do with the information? The only reason I ask is that they don't reconcile with your opening statement. Would you purchase a gage or a set of them? What would you do if you thought your rifle was out of spec. Further confusing the issue is the inference that a headspace gage should be able to measure other dimensions of the chamber. If headspace is critical to the psychology of the relationship with your rifle, wouldn't it be wise to have the headspace checked before you purchased it?

Fact is, spent cartridge cases will tell you everything you need to know about the headspace of a particular rifle for free. Popped or pierced primers being the most obvious.
GHPorter  [Team Member]
10/9/2010 8:22:13 AM EST
Originally Posted By CAC01:
Originally Posted By GHPorter:
Firstly, I know that "you shouldn't need to check headspace on an AR barrel and bolt." This of course assumes that your new barrel and new bolt are actually made to be within specs-which is apparently a problem in some cases.

My question is about which gauges to consider purchasing. Since every single headspace gauge I've ever seen is exclusively built to measure JUST the headspace, leaving the neck, freebore and leade completely out of the picture, is there any reason to go only with .223 Remington gauges or only with 5.56mm gauges? Is the SAAMI standard for headspace measurably different from the NATO standard? Is there one specific brand of gauges that is actually superior to others? Finally, is there a reliable, quality set of gauges that is made with an extractor cutout so that headspace testing could be done without disassembling the bolt first?

Thanks!


All good questions. If they could be answered to your satisfaction, what would you do with the information? The only reason I ask is that they don't reconcile with your opening statement. I said in my intro that new parts SHOULD be perfect, but indicated that sometimes this isn't the case. How does that not jive with wanting the tools to measure headspace?

Would you purchase a gage or a set of them? A "GO" and "NO GO" gauge should be effective for my uses-determining whether or not a particular combination of bolt and barrel were in fact properly headspaced together.

What would you do if you thought your rifle was out of spec. If a rifle I already owned was out of spec, I'd look into seeing whether it was the bolt or barrel that was the problem (lots of ways to do that) and replace the problem part.

Further confusing the issue is the inference that a headspace gage should be able to measure other dimensions of the chamber. I don't get you here. I said that since they ONLY measure headspace, was there any difference in the headspace standards for a SAAMI .223 Remington chamber and a 5.56mm NATO chamber. Different datum points, different tolerances, that sort of thing.

If headspace is critical to the psychology of the relationship with your rifle, wouldn't it be wise to have the headspace checked before you purchased it? Maybe I want to determine whether a replacement bolt is safe in a given rifle? Maybe I want to build a completely new rifle and want to assure myself that the parts I'm using are safe together?

Fact is, spent cartridge cases will tell you everything you need to know about the headspace of a particular rifle for free. Popped or pierced primers being the most obvious. [blue]I like to be assured that, when I put a rifle together, or replace a part, the rifle will be safe BEFORE I CHAMBER A ROUND. I also perform function checks before I load a rifle for the same reason-I want to know the thing is safe before I ever get to the range.


Milo5  [Member]
10/9/2010 9:05:20 AM EST
Assume nothing.
I have received factory new barrels that were supposed to be chambered and headspaced, ready to go, that were not finish reamed.
There is no such thing as a drop in bolt and barrel that will perfectly headspace each and every time.

The Army required us to headspace every bolt and barrel or combination job we did as repairman, why wouldn't you do the same in the civilian world? Because someone on the internet said you don't have to?

Fully half, if not more, of the people who post stuff like that have never field stripped or even handled a real AR15/M16 much less replaced a barrel on one, the other half are simply too careless and this will reach up and bite them someday if not already.

If you know the chamber dimensions of the barrel you are headspacing choose the appropriate gages, .223 or 5.56 NATO.
If you don't, at least use a Colt dimensioned field test gage which will tell you at the very least, whether the rifle is at a level of safe to fire headspace.HTH
CAC01  [Team Member]
10/9/2010 9:37:49 AM EST
Originally Posted By Milo5:
Assume nothing.
I have received factory new barrels that were supposed to be chambered and headspaced, ready to go, that were not finish reamed.
There is no such thing as a drop in bolt and barrel that will perfectly headspace each and every time.

The Army required us to headspace every bolt and barrel or combination job we did as repairman, why wouldn't you do the same in the civilian world? Because someone on the internet said you don't have to?

Fully half, if not more, of the people who post stuff like that have never field stripped or even handled a real AR15/M16 much less replaced a barrel on one, the other half are simply too careless and this will reach up and bite them someday if not already.

If you know the chamber dimensions of the barrel you are headspacing choose the appropriate gages, .223 or 5.56 NATO.
If you don't, at least use a Colt dimensioned field test gage which will tell you at the very least, whether the rifle is at a level of safe to fire headspace.HTH


Its 5 O'clock somewhere... Like your sphincter, you couldn't find headspace with both hands.
Old_Painless  [Moderator]
10/9/2010 9:50:29 AM EST
Cut out the insults or I will lock the thread.

This is a Technical Forum. If you can't add to the discussion, then don't post.


Gregory_K  [Member]
10/9/2010 10:19:05 AM EST
This is all I use.
M16 Maximum Headspace Gage, Ordnance Part Number 7799734, NSN 4933-00-070-7814. Disassembly of bolt not needed, gage is cut for extractor and ejector clearance.

Got it years ago from Bill Ricca.
Couch-Commando  [Team Member]
10/9/2010 10:22:33 AM EST
All I will say is that I've never changed barrels, and have shot one AR15 to hell. I've never checked headspace, and I've never blown myself up.
j3_  [Team Member]
10/9/2010 3:36:59 PM EST
Wheeler made some gages you could check headspace without bolt disassembly but they quit selling them. Midway had them for a while.
I bought one but I was not impressed the shoulder portion is a curve.
Milo5  [Member]
10/10/2010 12:55:00 AM EST
Originally Posted By CAC01:
Originally Posted By Milo5:
Assume nothing.
I have received factory new barrels that were supposed to be chambered and headspaced, ready to go, that were not finish reamed.
There is no such thing as a drop in bolt and barrel that will perfectly headspace each and every time.

The Army required us to headspace every bolt and barrel or combination job we did as repairman, why wouldn't you do the same in the civilian world? Because someone on the internet said you don't have to?

Fully half, if not more, of the people who post stuff like that have never field stripped or even handled a real AR15/M16 much less replaced a barrel on one, the other half are simply too careless and this will reach up and bite them someday if not already.

If you know the chamber dimensions of the barrel you are headspacing choose the appropriate gages, .223 or 5.56 NATO.
If you don't, at least use a Colt dimensioned field test gage which will tell you at the very least, whether the rifle is at a level of safe to fire headspace.HTH


Its 5 O'clock somewhere... Like your sphincter, you couldn't find headspace with both hands.


I rarely drink, never to the point of intoxication, and still carry 1 mil liability for $170 a month because in 22 years I have never had a claim filed by any customer.
It's your rifle, do what you want.
SchlaffTablett  [Team Member]
10/10/2010 1:23:21 AM EST
"Shouldn't have to" is kind of a BS statement that's fed into by manufacturers who tout "mil-spec" as the end all be-all and make it seem like every single piece they produce is measured to and within .0005". Fact is that it just doesn't work that way. Even with mil-spec they only have to test a lot sample not every piece. If you're willing to roll the dice feel free but you're going to feel pretty dumb when you blow up a rifle because you didn't headspace.

Now to answer your question(s)..
- Yes, headspace gauges only measure case dims, mainly OAL between the datum line (pre-determined point on the case shoulder) and the end of the case head. The reason .223 and 5.56 are different in many cases is because the allowable headspace is (or rather can be) different based on use. AS an example, a .223 gauge set is going to give you the optimal headspace for commercial .223 ammunition. The difference between SAAMI GO and NO GO on a rifle is usually +/- .003. When you start looking at military weapons (5.56) the tolerances open considerable to allow for variances in ammo production, quality, and even dimension. The tolerances can generally be assumed to be more generous with a 5.56 gauge set because of this. Is it any less safe? No, but it may contribute to a less accurate weapon.

-Look here for dims

-As far as gauge quality goes, probably not much difference between manufacturers so long as they are SAAMI compliant. Personally, I use Forster but that's just because I happen to like them. No real tangible reason why I suppose, I just do.

-There are some that are made with the cut out, but if they don;t have it, nothing says you can't make it yourself.
GHPorter  [Team Member]
10/10/2010 4:54:10 AM EST
Originally Posted By SchlaffTablett:
"Shouldn't have to" is kind of a BS statement that's fed into by manufacturers who tout "mil-spec" as the end all be-all and make it seem like every single piece they produce is measured to and within .0005". Fact is that it just doesn't work that way. Even with mil-spec they only have to test a lot sample not every piece. If you're willing to roll the dice feel free but you're going to feel pretty dumb when you blow up a rifle because you didn't headspace.

Now to answer your question(s)..
- Yes, headspace gauges only measure case dims, mainly OAL between the datum line (pre-determined point on the case shoulder) and the end of the case head. The reason .223 and 5.56 are different in many cases is because the allowable headspace is (or rather can be) different based on use. AS an example, a .223 gauge set is going to give you the optimal headspace for commercial .223 ammunition. The difference between SAAMI GO and NO GO on a rifle is usually +/- .003. When you start looking at military weapons (5.56) the tolerances open considerable to allow for variances in ammo production, quality, and even dimension. The tolerances can generally be assumed to be more generous with a 5.56 gauge set because of this. Is it any less safe? No, but it may contribute to a less accurate weapon.

-Look here for dims

-As far as gauge quality goes, probably not much difference between manufacturers so long as they are SAAMI compliant. Personally, I use Forster but that's just because I happen to like them. No real tangible reason why I suppose, I just do.

-There are some that are made with the cut out, but if they don;t have it, nothing says you can't make it yourself.
Thanks for your excellent information. Your observation of the validity of "shouldn't have to" tracks my own knowledge of statistical QA and experience with interchangeable parts that don't interchange.

Now a practical, two-part question: it's my understanding that a "NO GO" gauge indicates insufficient headspace while a "GO" gauge indicates sufficient headspace. Is my understanding correct, and how would one use a "GO" gauge to determine excessive headspace?

Gregory_K  [Member]
10/10/2010 5:55:52 AM EST
Dont think you can.
My guess
If the bolt does not close on the go you know headspace is short.
If the bolt closes on the go you know it might be good. As it can still be long.
If the bolt does not close on the no-go but closes on the go your good to go.
If the bolt closes on the no-go and go then it is time to swap parts.
Bretshooter  [Member]
10/10/2010 6:48:45 AM EST
Originally Posted By GHPorter:
Now a practical, two-part question: it's my understanding that a "NO GO" gauge indicates insufficient headspace while a "GO" gauge indicates sufficient headspace. Is my understanding correct, and how would one use a "GO" gauge to determine excessive headspace?



Small pieces of shim stock on the bolt face?
Gatorhunt  [Team Member]
10/10/2010 7:11:42 AM EST
I picked up the clymer go and no go gauges

http://www.clymertool.com/catalogue/ClymerCatalogueVol11.pdf

Quoted from the above link
SAAMI generally allows .010” between the
minimum and maximum values for rimless calibers. Clymer “GO” and “FIELD” gauges correspond
to the SAAMI minimum and maximum respectively. Because many feel that .010” is too much
variation between a minimum and maximum chamber, we also offer as standard a “NO-GO” gauge,
which is .006” longer than our “GO”.
Milo5  [Member]
10/10/2010 7:38:05 AM EST
Originally Posted By GHPorter:
Originally Posted By SchlaffTablett:
"Shouldn't have to" is kind of a BS statement that's fed into by manufacturers who tout "mil-spec" as the end all be-all and make it seem like every single piece they produce is measured to and within .0005". Fact is that it just doesn't work that way. Even with mil-spec they only have to test a lot sample not every piece. If you're willing to roll the dice feel free but you're going to feel pretty dumb when you blow up a rifle because you didn't headspace.

Now to answer your question(s)..
- Yes, headspace gauges only measure case dims, mainly OAL between the datum line (pre-determined point on the case shoulder) and the end of the case head. The reason .223 and 5.56 are different in many cases is because the allowable headspace is (or rather can be) different based on use. AS an example, a .223 gauge set is going to give you the optimal headspace for commercial .223 ammunition. The difference between SAAMI GO and NO GO on a rifle is usually +/- .003. When you start looking at military weapons (5.56) the tolerances open considerable to allow for variances in ammo production, quality, and even dimension. The tolerances can generally be assumed to be more generous with a 5.56 gauge set because of this. Is it any less safe? No, but it may contribute to a less accurate weapon.

-Look here for dims

-As far as gauge quality goes, probably not much difference between manufacturers so long as they are SAAMI compliant. Personally, I use Forster but that's just because I happen to like them. No real tangible reason why I suppose, I just do.

-There are some that are made with the cut out, but if they don;t have it, nothing says you can't make it yourself.
Thanks for your excellent information. Your observation of the validity of "shouldn't have to" tracks my own knowledge of statistical QA and experience with interchangeable parts that don't interchange.

Now a practical, two-part question: it's my understanding that a "NO GO" gauge indicates insufficient headspace while a "GO" gauge indicates sufficient headspace. Is my understanding correct, and how would one use a "GO" gauge to determine excessive headspace?



One would use a No-Go and/or a Field Gage to determine excessive headspace.
If the bolt does not close on a Go Gage, it indicates you have insufficient headspace.
If the bolt closes on a No Go Gage, it indicates you have excessive headspace.
If the bolt closes on a Field Gage, DON'T FIRE THE WEAPON! You have over maximum excessive headspace which can lead to case seperations and worse. HTH
SchlaffTablett  [Team Member]
10/10/2010 9:18:08 AM EST
Those guys pretty much summed it up as far as usage goes although even if Clymer says .010, common rifle chambers are about +/-.003. If you only have a GO gauge, the simple way (although not perfect) is to stick a piece of masking tape to the end of it. Thin masking tape like the blue painters tape and similar are about .003-.005" thick and make up the difference fairly effectively. If you stick on more than 1 thickness and it still closes, I'd go and find a real NO GO and double check it. One thing about that is to make sure only the bottom surface of the gauge is taped and make sure it's flat and not wrinkled. I'll also mention here that you should NEVER close the action on a headspace gauge under spring tension. For an AR, pop off the upper, swab out the chamber completely (I use q-tips or a rag with Simple green to make sure there's nothing in there), hold it parallel to the ground and slide the gauge in. Then ease the bolt/carrier into the upper (assuming you already took off the extractor) and gently but firmly try to push it home. It should close easily on the GO. Next, put in your NO GO or taped GO and do the same. Your bolt should stop short of lug engagement. It may go in and JUST start to turn but I mean JUST.

I know I'm long winded, but I want to make sure anyone reading this would understand the proper method to use. If you have any other q's feel free to PM if you like.
chris65  [Team Member]
10/14/2010 5:48:10 PM EST
[/quote]
One would use a No-Go and/or a Field Gage to determine excessive headspace.
If the bolt does not close on a Go Gage, it indicates you have insufficient headspace.
If the bolt closes on a No Go Gage, it indicates you have excessive headspace.
If the bolt closes on a Field Gage, DON'T FIRE THE WEAPON! You have over maximum excessive headspace which can lead to case seperations and worse. HTH[/quote]

Giving Milo a +1 here and on ALL of his posts in this thread.

And a bump for others to see...
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