I have bought 5 AR barrels at one point or another, 4 of them cheap, one of them less, but still fairly cheap, and all of them had their headspace set to a standard GI bolt (Bolts, and extensions have standards). All shot fine, none stretch cases. I have never seen an AR barrel that did not have the headspace set, unless it came without an extension. Where are you finding these?
Checking Headspace on AR-15 Rifles
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Tolerance stacking can lead to a particular bolt/barrel combo not having sufficient headspace--e.g. the bolt head is at the minimum or maximum depth while the barrel is the reverse and so on. Yes there are standards, but the practicalities of manufacturing are that they replace machine tools on a certain schedule based on wear--as long as the range is within plus/minus of the tolerance band around the std., everything is copacetic. With two components-bolt and barrel, both have to be within the tolerance range which for an individual rifle is set by the go (fails go gage, your headspace is too short) and closing on no-go gauge (too long on headspace).
Headspace doesn't come solely from the barrel--it is the combination of the distance from the bolt head when locked to the reference line on the case shoulder (for unrimmed cases)--rimmed cases are different and based on the rim only (.22 rimfire for example), some pistol cartridges from the case mouth, and belted magnums are different as they headspace from the belt.
I get all of that, but my understanding was that the AR, along with all the modern military rifles are parts interchangeable (simple armory rebuild), and any stacking translates to failure to meet specification. A max dimension bolt made on worn out equipment (oversize) against a maximum dimesntion extension made on worn machinery (also oversize) and headspaced on a smaller bolt would still have you in the correct range to work with all correct bolts. At least thats what I thought.... Now as far as actual products... maybe not. There will always be issues, and not everyone is going to scrap a part (I recently had a receiver hole/bolt release stack up, and need work), but it should not be a major issue. Not doubting it is an issue, just wondering if this is a new thing with all the over production going now. BTW sorry for the underline.. its not by intention, some kind of error on the text.
Think about it this way--uppers and lowers from different manufacturers do not always play nicely with each other, some use different pins, etc. People expect tolerance stacking all other supposedly mil-spec parts (pins, triggers, guards, handguards) on the AR but don't expect any on barrels and bolts. IT happens.
It is not common and a lot of people have gotten away with not using headspace gages on builds. Read Pat Sweeney, Kevin Miramatsu, or Glen Zediker if you like for their take on it. Others avoid it by buying the barrel and bolt from the same place and having them check the headspace. If you have the gages, then you can buy from a place with a good return policy. When it does occur, you can limp along with too long headspace as long as it is within field range--if you don't reload, you may not notice it. You can also rent a pair of them from Reamers 4 Rent and a few other places for less than $20.00 for a week (not counting deposit and mail).
If you are a experienced reloader, you can size your brass specifically for that chamber (either through fireforming if the headspace is really long or by using once fired brass from that particular rifle). Either way, you may have cartridge separations which aren't that pleasant in a semi-auto (it has happened that a new cartridge is crammed into the remnant of the fired one where a complete separation has occurred or at best shortened brass life).
Too short headspace also can occur due to tolerance stacking and it can be kaboom bad depending on the load, temperature, throat, etc. It can be cured by simply reaming the chamber out with a finish reamer but you will still need the go gage to tell you when you have gone far enough and a no go to check that you did not go too far. (if it is a carbon moly only--chrome or nitride (melonite) chambers will destroy the reamer. The problem with using ammo as a go gage is that ammo makers do the same thing with their dies especially on blaster quality ammo--that is one of the reasons that blaster level ammo can be cheaper is that reaching SAAMI or CIP tolerance is "good enough". Careful handloaders can usually avoid that problem and some actually prefer "tight chambers" that are at a bare minimum. That is why when buying used, have the rifle checked thoroughly either by yourself if you have the tools or by a gunsmith, especially if you don't know the seller and cannot ask them questions. I did not mention the field gage for a reason--they are for used rifles to determine whether the headspace is long enough to be considered unserviceable.
If you buy a new complete AR from a known manufacturer, you probably will not have a headspace problem aside from one company with a rather infamous collection of monkey mechanics on a bender. If you buy parts at the gunshow or from whoever is cheapest on the internet, then I would definitely buy the gages (less than $60 for the pair). The bolt ejector removal tool is useful whenever you decide to clean the bolt or replace springs and is worth the $30 or so that you can find them for and you will need that if you don't have the military gages (Bill Ricci (good guy actually for some parts) was the last that I knew who had them and he charged $75 per gage several years ago pictured above). Be aware that mil-spec is not the same as GI Issue on gages and also make sure that your gages come from the same mfg (e.g. don't mix a forster with a clymer gage. )
BBBBill
Member
The key word here is military. The bulk of these guns are not being made for the military, so standards in effect for military production may not apply. The other issue is the huge number of manufacturers of parts and complete guns. The more you have, the more possible ideas about what is acceptable. Very much like the 1911 pistol. With that gun there are no drop in parts and one time that you can safely assume that fitting will be required.
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Chuck R.
Member
I have had one bolt/barrel combo that closed on a No-Go gauge, but would not close on a "Colt field gauge", meaning that the combo was on the edge of excessive headspace. Same barrel with different bolts would not close on the No-Go, the bolt in other barrels still would close. I contacted the BCG manufacturer and they sent out a new bolt.
After that I'm firmly in the "Check your headspace camp". At a minimum I'd at least get a 5.56 "Field gauge", cheap insurance at around $25.
Chck
After that I'm firmly in the "Check your headspace camp". At a minimum I'd at least get a 5.56 "Field gauge", cheap insurance at around $25.
Chck
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