Are AR barrels sold with receiver extentions always properly headspaced?


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Arizona_Mike
January 20, 2014, 12:24 PM
Can I assume that any AR-15 barrel sold by a reputable vendor with the receiver extension already attached has proper head space? Has anyone ever encountered one that was not?

Mike

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jdh
January 20, 2014, 12:55 PM
If it comes with the bolt and the seller says the bolt barrel set has been checked for head space. Otherwise check it before you shoot it.

taliv
January 20, 2014, 02:19 PM
I've seen them worn out but never wrong from factory. Not saying it doesn't happen.

lencac
January 20, 2014, 02:27 PM
I've put together a number of AR's with barrels and bolts from different venders and I always check headspace. So far they have all checked to be darn near perfect.
Which, when you think about it is quite impressive all by itself :eek:

Walkalong
January 20, 2014, 02:27 PM
If everything is in spec, barrel, ext, bolt, it should be OK, but never say never. Tolerances can stack up against you.

MistWolf
January 20, 2014, 03:00 PM
The only way tolerances can stack against you is if the manufacturer is using poor processes.

The way the AR is designed to be built, the bolt and receiver extension will fall within allowable limits for headspacing

Walkalong
January 20, 2014, 05:57 PM
Correct. We said the same thing. :)

Grunt
January 20, 2014, 11:21 PM
Even in the military where we get parts from one vendor, we always check headspace when swapping out a bolt. I mean, really, is the price of a gauge so high as to risk destruction of your AR at best and you or your friend or family member being maimed or killed at worst? While I've never seen an AR-15/M-16 fail a headspace check, one blowing up because I wanted to take a short cut and save a few bucks will NOT happen on my watch!!!

Arizona_Mike
January 21, 2014, 11:50 AM
It always puzzles me how people try read between the lines.

1. I would not be asking if I wasn't concerned and did not understand the importance of headspace.

2. I'm not looking to make shortcuts. The first clue that I'm not looking to make shortcuts is that I am asking the question.

3. It's $8 to rent a gauge set so I'm definitely not looking to save "a few bucks".

Mike

jdh
January 21, 2014, 04:42 PM
Remember what President Reagan said "Trust but Verify". Still a good policy even if we are not referring to nukes.

gotigers
January 21, 2014, 08:02 PM
Im with Taliv. Never seen one not headspaced from the factory.

If both the bolt and barrel are new, I don't worry about it.

MistWolf
January 22, 2014, 12:06 AM
You can verify the headspace with a round of factory ammo

briansmithwins
January 23, 2014, 08:10 AM
You can verify the headspace with a round of factory ammo

How exactly do you check for excess headspace with a round of ammo?

I have a FIELD gauge and check my rifles yearly.

BSW

Tirod
January 23, 2014, 11:39 AM
Most shooters never ever check the headspace on their firearms. I suspect you couldn't get them to accurately explain it.

A custom barrel assembler will check it, and can headspace to a bolt they supply as a matched assembly. But like was said, gauged or not, it's rarely if ever a problem. Bolt bounce unlocking the action because of improper dynamics causes more issues.

The barrel extension feature of the AR15 is really it's most important feature, and has become a milestone in the evolution of gun design. Compare it to a traditional firearm: the receiver has the matching lugs to anchor the bolt, the barrel is pressed into it, and the headspace is checked when assembled. That is gunsmith level work done on expensive machinery and slow to accomplish.

The AR barrel extension has the lugs in it, it screws onto the barrel, and the headspace is adjusted like a micrometer -you turn it on the threads to get it right. No press, no heavy receiver, and it doesn't take a gunsmith, just a trained assembler. Precisely the kind of thing that an team of engineers designing a gun for mass production would come up with, a low labor cost operation. It also allows using an alloy receiver, which considerably cuts the costs of making the firearm.

The Browning BLR uses the same design, a barrel extension anchored in an alloy receiver. Lever action or direct impingement, the real landmark improvement is the barrel extension.

Since it's a mass production operation with no press or machine shop training to do it, it can deliver accurate results more quickly with less set up and a higher thruput. While no maker is willing to slack on getting headspace done right, it's so much easier to do the threaded barrel extension that somebody would have to go out of their way to screw it up.

That's why a barrel with extension from a vendor on one coast, and a bolt from the opposite coast, never having been matched, can and do work well. Another is the vendors sticking to the same blueprint and tolerances because of established specs. If they want to sell it to the military, they build it right and don't ship out of spec parts.

I have to ask - are milspec M16's headspaced with matching bolts on the line? Don't know. But the procedure in the field is to check the headspace, if it's Nogo, then replace the bolt and check again. If it's still Nogo, then replace the barrel and test with the old bolt. If it's still Nogo, then use the new bolt.

In other words, an orderly method of just trying combinations of parts until they match. The field repairs do not attempt to reset the barrel extension. The reason is that when the headspace is set, the extension is pinned by driving it into the threads, locking it. Then the feed ramps are cut and the gas port drilled - twisting the barrel extension after that messes up the vertical indexing and creates more work.

With a manual action like the BLR, a front sight post would get rotated off vertical.

I bought my barrel with matched headspaced bolt. If I was the Man With No Name who walked into a rustic AR store and hand picked the parts to assemble the gun, I would give it little regard. Test firing it would reveal it was likely spot on.

That's the Good, Bad, and Ugly about it.

rodregier
January 23, 2014, 12:43 PM
Anything manmade has the possibility of a defect :-(

briansmithwins
January 23, 2014, 06:45 PM
The AR barrel extension has the lugs in it, it screws onto the barrel, and the headspace is adjusted like a micrometer -you turn it on the threads to get it right.

From what I've read that's not how AR barrels are made. The barrel extension is screwed onto the barrel to hit a specific torque. The chamber is then finished reamed to match the barrel extension. Then the index pin and gas port hole are drilled. The barrel would then be hardchromed if called for.

You can't replace barrel extensions on a finished barrel since you'll almost never get the right torque value while having everything line up.

BSW

hentown
January 23, 2014, 07:28 PM
So far, a couple of "experts" who've never seen an AR fail a headspace check, using new parts, have recommended, nevertheless, the superfluous checking of headspacing. How would one propose to the newbie that he adjust the headspacing, anyhow? Inquiring minds want to know. ;)

I'm not at all careless about firearms, but I just wasn't raised to make illogical, fear-based decisions.

I've built a bunch of ARs. Will probably build some more, and I'll NEVER check for proper headspace, when assembling an AR of new parts that were acquired from reputable sources.

jdh
January 23, 2014, 07:41 PM
It was made by man.
Man is an imperfect creature.
Therefore nothing made by man can be perfect.

You can check ten, a hundred, or a thousand and they all pass. A bad part that slips through QC gets put in the next one. The rifle fails because you thought it a waste of time to check it. Your professional reputation is now forever damaged.

A head space check takes maybe 5 minutes if you take your time. Cheap insurance.

BTW, how have "they" never seen the head space is not correct if "they" have not taken the time and effort to check it?

Bartholomew Roberts
January 23, 2014, 08:36 PM
I've seen a factory Nesard upper (yes, a while ago) with improper headspace. So it does happen, albeit rarely.

MistWolf
January 23, 2014, 11:24 PM
How exactly do you check for excess headspace with a round of ammo?

I have a FIELD gauge and check my rifles yearly.

BSW

In a safe manner, use a factory round in the same manner as you would a headspace gauge. If it's too tight, you'll feel it. If there's no resistance at all, you may need to investigate further. You can use pieces of cellophane tape on the bottom of the brass to measure how much extra space you have (I forget how thick cellophane tape is but you can use it pretty accurately). I've headspaced a of a couple of FALs using factory ammo to set the locking shoulder. Later, when I was able to borrow a go/no go gauge, it measured fine.

The biggest problem is chamber headspace that's too long. It can cause cases to split at the shoulder and light primer strikes. It can also give false high pressure signs as the case will seal the chamber with a gap between the bolt face and the primer will back out. The same can actually happen with loads that don't make enough pressure.

Next problem is chamber headspace that's short and won't allow the bolt to go into battery.

After checking the headspace with a factory round, fire a round and compare the spent case to another factory round and see if the shoulders are pushed out excessively.

For those who haven't figured it out, it's safe to use factory ammo if the firing pin is removed. To make life easier, remove the ejector as well

Let me add I'm not suggesting this method to replace the use of a field gauge, but with a bit of common sense, it can get you up & running with a new rifle

Float Pilot
January 24, 2014, 02:32 AM
Back when the Air Force had the not so brilliant idea to convert old 1964 vintage M-16s to something like an M-16A2, our shop was tasked with converting about 1,800 rifles. The kits came from the lowest bidder..

Out of the 1,800 new barrel assemblies, we had two or three that would not properly headspaced.

Lloyd Smale
January 24, 2014, 07:36 AM
another one that will say ive never seen one not good as is.

cfullgraf
January 24, 2014, 07:57 AM
So far, a couple of "experts" who've never seen an AR fail a headspace check, using new parts, have recommended, nevertheless, the superfluous checking of headspacing. How would one propose to the newbie that he adjust the headspacing, anyhow? Inquiring minds want to know. ;)



In my opinion, and with that and $5 you can get an overpriced designer coffee, the bolt/barrel headspace should be checked.

I can see the advantage to the manufacturing specs on an AR-15/M-16 rifle is the armorer in the field can quickly check various bolts in the barrel and does not need a reamer to make one fit. Chances are good, the first one will gauge correctly.

If an individual plans to build several rifles, the gauges become relatively inexpensive additions to the tool box.

If the individual is planning on only building one or two rifles, either buy from a vendor that will sell a head spaced bolt with the barrel, find a local gunsmith to do the check, or make an arrangement with a buddy to share the cost of the gauges.

It is cheap insurance in the long run.

Also, how do you think those fellows that have never or rarely seen a bolt out of spec? They have checked all the barrel and bolts.

Onmilo
January 24, 2014, 08:58 AM
Always always ALWAYS check barrel headspace before installing and shooting any barrel.
Never assume a barrel is properly headspaced to a specific bolt unless the builder or manufacturer sends a certificate stating that fact.

I have received several AR15/M16 barrels shipped as "Ready to go" that were not even finish chambered yet the barrel extensions had been installed.

Walkalong
January 24, 2014, 09:07 AM
Checking headspace with a factory round is guessing, and relies on the round being right, just like not checking it at all and relying on the maker to do it right.

Sooner or later, it will bite someone. The safe reliable answer is cheap. Or you hope yours is one of the 99% they got right.

wally
January 24, 2014, 11:21 AM
I have a FIELD gauge and check my rifles yearly.

BSW scores again!

These are the ones we all should have.

Temp430
January 24, 2014, 02:40 PM
Check your head space with a set of GO/ NOGO gauges. Or buy your barrel from a vendor that supplies a bolt with the proper head space. White Oak Armament, and others offer this as an option with their barrels.

Arizona_Mike
January 24, 2014, 05:02 PM
Just in case anyone is wondering how to use these gauges (I am new to ARs but not to building rifles in general): A new chamber should allow the Go gauge to close and the No Go gauge should not be able to close. A gun is considered safe as long as the Field gauge cannot close. If the field gauge can close, the gun should be taken out of service and repaired. Testing should be done using finger pressure with a stripped bolt. I've never done this on an AR (yet). I'm not sure human fingers can get sufficient purchase on a stripped AR bolt. Perhaps the whole carrier should be used.

Mike

barnbwt
January 24, 2014, 07:49 PM
Headspacing, as I understand it, has a few purposes, not all of them safety related;

1) When assembling a rifle, to ensure factory ammo will fit

This is the one most closely associated with safety, but it's importance (and consequences, especially) are a bit overblown on forums. The primary goal is to make sure common ammo will fit, so it doesn't need custom sizing for good function. Too tight, and the action jams or won't lock, too loose, and the poorly secured case causes all sorts of issues. Issues like extractor damage, excessive brass wear, and in extreme cases, case head separation. When worrying about the last one, do remember that high pressure delayed/straight blowback designs like the five-seven and G3 allow the bolt to move quite a bit (by micrometer standards) while the case is pressurized, and the arrangement is perfectly safe within reasonable limits. The case whose neck you bump back and crimp repeatedly isn't the wet tissue bag you think it is (nor a blown-glass light bulb). If the bolt closes, and the round doesn't rattle between the stripped bolt face and chamber, it's unlikely things will turn out uglier than you knocking back shoulders a bit more than you should really have to (slight exaggeration here, but not by much)

2) When inspecting a rifle, to monitor bolt set back

This is the one that is actually the most critical to safety where it can bite you. As a new rifle wears in, the mating/bearing surfaces wear and polish, and the bolt opens up a little. No big deal. Over the years, the rifle has a squib load or two, some hot handloads, and a goober who shot it full of water a few times as a misguided "torture test." Now the bolt measures a little bit longer, but not because of wear. Because the mating surfaces have actually deformed under excessive load, stretching the action, peening the lug faces, and bending the lug attachments. Depending on severity, it's something to keep in mind, but still not worrisome. If after another group of rounds, the head space continues to grow, now you have seriously bad trouble on the horizon; the overpressure damage is so great the action is unable to maintain its structural integrity at working load levels, and is in the midst of failing by fatigue mechanisms (micro cracking). That's when the gun becomes a wall-hanger or demands service.

3) To chase the illusive mayfly of "Accuracy"

As with all things pertaining to precision shooting, the more consistent you can be in all things, the better you can be. Knowing exactly where the headspace sits enables you to size your brass for the perfect consistent fit, and eliminate another of the extremely long list of variables in the equation.

In the interest of morbid curiosity, did any of the famous gun writers ever do an experiment in which they gradually deepened or widened the chamber while firing spec ammo to see just how bad, for example, an M1 Garand had to be before it would reliably rupture cases? For some reason I'm thinking this was done with 1903's by someone (Hatcher?) and that a fairly shocking amount of room was needed to pop the case (like .1" or something :what:)

TCB

MistWolf
January 24, 2014, 11:14 PM
Checking headspace with a factory round is guessing, and relies on the round being right, just like not checking it at all and relying on the maker to do it right.

Sooner or later, it will bite someone. The safe reliable answer is cheap. Or you hope yours is one of the 99% they got right.

...and relying on the headspace gauge maker getting it right as well. They don't always. If the ammo was that far out of spec, it would be a problem when you went to go shoot it.

Not saying folks shouldn't check, but how much of a problem is headspacing on ARs?

BSW scores again!

These are the ones we all should have.

Not to pick on BSW (because I'm not) but how will you check to ensure you don't have a short chamber with a field gauge?

JoePfeiffer
January 24, 2014, 11:32 PM
...and relying on the headspace gauge maker getting it right as well. They don't always. If the ammo was that far out of spec, it would be a problem when you went to go shoot it.
If it doesn't pass, you've got some investigating to do. Yes, there is some chance the rifle is OK and the gauge is off; the point is you can be sure that something is wrong.

To pass when the gauge is wrong requires both the chamber and the gauge be off in the same direction -- that's extremely unlikely.

barnbwt
January 25, 2014, 09:20 AM
"Checking headspace with a factory round is guessing, and relies on the round being right, just like not checking it at all and relying on the maker to do it right.

Sooner or later, it will bite someone. The safe reliable answer is cheap. Or you hope yours is one of the 99% they got right."

Technically, you'd rather the gun be headspaced to the ammo, rather than some arbitrary guage. If the ammo you intend to use is consistently under or oversized, the guage doesn't get you where you need to be. Fortunately, standards in the industry get the gauges/ammo close enough to eachother that any variance impacts accuracy rather than safety.

Anyone have a story of catastrophe by headspace? I'm curious how far out of whack these rifles are before the brass tears. I also note that the vast, vast majority of ruptures I've read abut came from bad ammo, obstructions, failure to lock up, and bolt lug failure (roughly in that order), with headspacing itself not figuring in any as far as I can remember :confused:

I have to wonder if this whole "check your headspace often and it has to be accurate to within a thousandth or so" thing arose from those Springfields that weren't properly heat treated and would stretch like Play-Dough until failure when shot; lord knows a lot of other conventional wisdom regarding safety traces back to a single batch of a single rifle (training Arisaka's tainting the whole group, for instance).

TCB

Walkalong
January 25, 2014, 09:40 AM
Technically, you'd rather the gun be headspaced to the ammo, rather than some arbitrary guage.
You would rather have the gun with proper mechanical headspace, and size your ammo to fit the gun.

The go, no go, and filed gauges are very carefully made, are used by gunsmiths all over the world, and are fairly easy to double check. A loaded round can vary a lot. Having more faith in checking the chamber with a loaded factory round than a no go gauge is incorrect thinking.

MistWolf
January 25, 2014, 01:49 PM
You would rather have the gun with proper mechanical headspace, and size your ammo to fit the gun.

The go, no go, and filed gauges are very carefully made, are used by gunsmiths all over the world, and are fairly easy to double check. A loaded round can vary a lot. Having more faith in checking the chamber with a loaded factory round than a no go gauge is incorrect thinking.

Loaded rounds don't vary by a lot.

I never said to place more faith in a factory round. I simply said that using a little common sense, you can verify the headspace of your AR is safe with quality factory rounds. It's what you do anytime you use different ammo anyway, check the fit before firing. The method is close enough that I was able to set the headpsace in a couple of FALs that way, later verified when I was able to hook up with a fellow FAL owner with gauges.

There was a thread about headspace gauges over on the FAL Files where it was brought up that you need to be careful which gauges a builder should use because one manufacturer's gauges gave different results than others. It was also brought up that for more consistent readings, do not mix gauges from one make with another- Do not use a GO gauge from one maker and a NO GO from another. Variations do exist

jgr_lv
March 13, 2014, 02:20 AM
:what:Guys, as far as I'm concerned, assuming a bunch of parts made by different companies on different days will fit together with all the critical tolerances within spec ranks up there with assuming a gun isn't loaded. This is why they make headspace gauges and why reputable gunsmiths use them. You may very well get lucky, but do you really want to bet any portion of your anatomy on it? Seriously? You don't assume anything; you check everything, just like you check whether or not the hammer will push off full cock and that the safety works. You did do that, didn't you? If not, tell me when you plan to take this thing to the range so I can stay home that day. If you're going to spend the money to buy all the parts to build an AR, spend another twenty or so on The AR-15 Complete Assembly Guide by Walt Kuleck and Clint McKee, read it and follow the directions. When you're done, if you don't want to spend another sixty bucks or so for a set of headspace gauges, take your work to a real gunsmith and ask him to check it. Anything else is like spending the money to build yourself a race car and, on track day, cheaping out and driving it on retreads. You might survive to learn from the experience, maybe.

jr_roosa
March 13, 2014, 10:33 AM
In the interest of morbid curiosity, did any of the famous gun writers ever do an experiment in which they gradually deepened or widened the chamber while firing spec ammo to see just how bad, for example, an M1 Garand had to be before it would reliably rupture cases? For some reason I'm thinking this was done with 1903's by someone (Hatcher?) and that a fairly shocking amount of room was needed to pop the case (like .1" or something )

Yep. It's in his notebook.

It's also in there that mil spec 30-06 ammo can easily run longer than a mil spec chamber. My garand with a chamber that is in the middle of the mil spec range will knock the shoulder of a properly sized round back about 0.005" and will resize HXP rounds that run a tad longer than they should. That's just with chambering the round.

He writes that certain machine guns need ammo with shoulders longer than the chamber to avoid head separation because of this issue.

There are also many reports of people accidentally shooting 7.62 rounds in a 30-06 with about 1/2" of excess headspace. You get a funny looking fireformed case and not much else.

Also, case head separation or a split shoulder is really a non event. Even more of a non event if you have a broken shell extractor in your range bag. In combat, a broken shell in the chamber would be a very bad thing, but only because it takes the weapon out of service. That's one reason the military has religion on avoiding long headspace.

The scary thing you want to avoid is a really short chamber that won't accept the round. It would need to be so short as to give you an out of battery slam fire.

I know the head spaces on all my rifles to within a thou or two. If I weren't hand loading I probably wouldn't care so long as they could easily chamber a factory round. Who cares if the brass gets fireformed a little long if I were never using it again anyway?

J.

Blade First
March 14, 2014, 08:05 PM
Interesting 'what if' discussion but more entertaining than practical re: AR-15 rifles.

If you purchase parts from a reputable mfr. [and the ones who don't hold decent tolerances are out of business in short order] then proper headspace is only an issue if you start mixing and matching bolts and chambers amongst different uppers.

And even then, a "used" bolt in a brand new chamber might headspace just fine...or vice versa. Virgin bolt in virgin chamber...should be good. Ah, the joys of youth.

However, gauges are inexpensive insurance if you consider the possible consequence of grossly out-of-spec parts. And gauges last a looooong time.

Buy...and measure wisely...if you choose, but I can't recall a single problem re: headspace in the last few decades where new, good-quality parts were used in rifles I handled.

kilibreaux
March 15, 2014, 05:32 AM
Maybe I should lie awake all night pondering this latest question of the ages.

The FACT IS, the AR-15 headspaces within spec from the factory!

While ONE might find an out-of-spec headspace on a single example, MOST AR-15's headspace within spec...actually, in 30+ years of putting AR's together I've NEVER found a headspace issue....for whatever it's worth.

It's a shame because IF we could find a huge number of AR's out of spec for headspace we just might be able to bring back the 7.62x51 M1A1! Sure the difference is that HS on an M1A1 must be set by a person well-trained and qualified for EACH AND EVERY EXAMPLE, whereas the AR headspace is set at a factory to such a degree of precision that virtually NO bolt won't fit...

Yeah, let's go back to the process of barreling receivers and setting headspace off the receiver like the M-14....sure it's technologically ridiculous and of zero value, but hey, if it undercuts the popularity of that up-start AR-15 (57 years of popularity) then we NEED to do it!

briansmithwins
March 15, 2014, 09:41 AM
The FACT IS, the AR-15 headspaces within spec from the factory!

Which factory?

Colt? FN? Century Arms? Hesse? Jim-Bob's Discount Gunz & BBQ?

BSW

M1key
March 15, 2014, 10:19 AM
For whatever it's worth...

http://www.thehighroad.org/showthread.php?t=743034



M

Bartholomew Roberts
March 16, 2014, 02:57 PM
For whatever it's worth...

http://www.thehighroad.org/showthread.php?t=743034

Headspace was still good though, right? ;)

M1key
March 16, 2014, 03:47 PM
Headspace was still good though, right? ;)
On the replacement barrel?...yes

M

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