Arizona_Mike
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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
Mike
Are AR barrels sold with receiver extentions always properly headspaced?
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Grunt
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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
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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
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
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briansmithwins
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How exactly do you check for excess headspace with a round of ammo?
I have a FIELD gauge and check my rifles yearly.
BSW
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.
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
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Anything manmade has the possibility of a defect :-(
briansmithwins
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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
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.
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.
fire the factory rd, using a string to pull the trigger
with the gun tied off to something heavy. Mike the fired case, and compare to specs online, or with a case from a known-good gun/ammo. If the case is bulged, or "stretches" more than normal at the shoulder, or flows more brass into the neck than nomal, something is not right with that gun/ammo combo.
with the gun tied off to something heavy. Mike the fired case, and compare to specs online, or with a case from a known-good gun/ammo. If the case is bulged, or "stretches" more than normal at the shoulder, or flows more brass into the neck than nomal, something is not right with that gun/ammo combo.
jdh
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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?
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
Member
I've seen a factory Nesard upper (yes, a while ago) with improper headspace. So it does happen, albeit rarely.
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
Member
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.
Out of the 1,800 new barrel assemblies, we had two or three that would not properly headspaced.
Lloyd Smale
Member
another one that will say ive never seen one not good as is.
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.
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.
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.
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