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Why do I need headspace gauges for an AR build? Login/Join 
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Picture of Rustpot
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I built many without checking headspace. After getting my gauges I checked everything I had and found no issues. I've had it come up once, personally, and it was a 5.56 marked barrel that didn't pass 5.56 go, but did pass .223 go, that probably would have functioned.

Headspace being out of spec in the AR can result in function issues, accelerated wear, poor accuracy, damaged brass, popped primers, and other non-catastrophic issues. It has to be VERY bad to actually cause safety issues.

How many people with ARs have shot them a bunch? How many people do you know with cheap guns that have intermittent issues, or issues with weak ammo, hot ammo, or some other mix?

There isn't a widespread issue of bad headspace plaguing the AR world. There is a widespread issue of poor information, companies that shout "MIL SPEC" with no ability to actually hold tolerances and properly control their quality to ensure it meets spec, and the assumption that "just as good" means your $300 parts build is of the same performance and quality as a $1000 rifle built by a quality shop.

There are videos and photos out there of all kinds of wacky stuff. Anderson lowers in blister packs at a store with no magwell cutout is one of my favorites - "mil-spec is mil-spec, only 4 forges, just as good!"
 
Posts: 5822 | Location: Romeo, MI | Registered: January 03, 2009Reply With QuoteReport This Post
Freethinker
Picture of sigfreund
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Excellent comments, Rustpot; thanks.




“A man hears what he wants to hear and disregards the rest.”
— Simon & Garfunkel, The Boxer, 1970
 
Posts: 41486 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
fugitive from reality
Picture of SgtGold
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quote:
Originally posted by Rustpot:
quote:
Originally posted by SgtGold:
Here's some info on the need for, or lack there of, the extractor\ejector cut on a headspace gauge.

https://mansonreamers.com/2016...on-headspace-gauges/


They leave out the part where it's required for mil because not having them wears out your gauges if you don't disassemble the bolt. Gauges are not to be used under spring tension, that makes them into paperweights. You're also cramming a hardened steel gauge under your extractor rim, designed for soft metals- or heaven forbid snapping the extractor over the rim with the gauge in the chamber. And leaving the ejector in place means you need to fight the somewhat heavy spring and force the gauge into the chamber with extra pressure from the rear to seat the gauge as it drags across the wall of the chamber, which is also a terrible idea. Plus you're now extracting your precision gauge and skipping it across the barrel extension lug area as it tries to eject off the face.

None of these conditions are acceptable use for a ground, toleranced, precision gauge. I am baffled that a "precision" company would publish that. Perhaps they expect you to use it only a few times?

If it's a one and done scenario, have at it. I've used mine quite a bit, am considering pursuing armorer work as a side business, and I do not want to be pulling ejectors all the time, so I went with the modified gauges.


The gauging schedule varies, but some rifles don't see a headspace gauge for up to four years at a time. The gauges themselves however, are in almost constant use. I spent some time in depot level maintenance working with the full time small arms guys, and they just don't treat their gauges with the same reverence that you seem to suggest. It's not that the gauges are 'free', it's the fact that they're just not that fragile. The part of the gauge that's important to keep pristine is the shoulder cut at the very front. The idea that the gauge may scrape against the side of the chamber just isn't an issue because the amount of ejector spring pressure is minimal.


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Posts: 6555 | Location: Newyorkistan | Registered: March 28, 2007Reply With QuoteReport This Post
fugitive from reality
Picture of SgtGold
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quote:
Originally posted by sigfreund:
This is something that struck me in that article: “If the cartridge rim will slip under the extractor, the rim of the gauge will also.”

That is of course a big if. The cartridge case rim will “slip” behind the extractor hook of the so-called “controlled feed” bolt, but that extractor design is not used with all rifles. The extractor hooks of all my long guns, Sakos, Tikkas, M1A, and AR-types, all must snap over the case rim as the cartridge is chambered, and that would be necessary when using a headspace gauge if the extractor wasn’t removed.


The spring loaded extractor is designed to snap over the rim of the cartridge as the bolt closes. This is an extremely reliable design that has been through billions and billions if not trillions of rounds in many different rifle and pistol designs. That being said you don't drop the bolt on a headspace gauge. There are sometimes just a few thousandths of an inch between pass and fail, and dropping to bolt can cause false readings.

The procedure I was taught only works if the ejector is either removed, you have a gauge with the rim rebated, or you have a receiver mounted ejector. The gauge is placed on the face of the bolt, under the extractor. The bolt is closed by hand, until any resistance is felt. In the case of an AR, you close the bolt carrier group by bushing against the back of the BCG with your thumb. You will feel two or three point of contact as either the locking lugs or the gauge shoulder contacts something. Apply a little more pressure and you'll quickly figure out if it's the bolt rotating shut, or it's the gauge solidly contacting the shoulder of the chamber.

There are some very specific gauges out there. One of them is an extension headspace gauge. It only measures the barrel extension itself, but it can help determine exactly what's out of spec.


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Posts: 6555 | Location: Newyorkistan | Registered: March 28, 2007Reply With QuoteReport This Post
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quote:
Originally posted by sigfreund:

And as I started this thread, I’ll drift off a bit by raising this point.
I don’t know how many hobbyists there are who assemble their own ARs or switch barrels, but I would guess that it’s significantly more than the number who also have and use headspace gauges (two conditions usually make the probability less than one condition). Perhaps I’m wrong, but if that’s true, and if confirming proper headspace is so important, why don’t we hear of more problems resulting from failure to do that?


If failing to confirm proper headspace is a dangerous practice and a significant percentage of AR barrels don’t have proper headspace, then why don’t we hear of the bad consequences? Do they happen and we just don’t hear about them? Does everyone check the headspace of their builds? (I know from personal experience that that’s not true, but perhaps it’s very rare.) Is there some other explanation?


The point is that though the rate of issues with AR-15 Headspace is pretty low it isn't Zero. I've had 2 AR-15's with chamber issues, one was a top tier Match rifle with a VERY tight chamber (and sold as such), the other was a cheap POS from a unlamentedly gone manufacturer that required a bolt swap to get into spec and function. I've had quite a few AR-15's but certainly less than 100. I would "guesstimate" the problem rate at maybe 1-2% or less. Again Very low but not Zero.

Normaly people could probably assemble a couple dozen AR's and never see an issue. It's UNLIKELY that there will be an issue. But again it's nice to KNOW that there is NOT a headspace issue with my rifles and we can move on to things like Properly staked bolt carriers etc etc........


Remember, this is all supposed to be for fun...................
 
Posts: 3836 | Registered: April 06, 2007Reply With QuoteReport This Post
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Picture of Rustpot
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quote:
Originally posted by SgtGold:
The gauging schedule varies, but some rifles don't see a headspace gauge for up to four years at a time. The gauges themselves however, are in almost constant use. I spent some time in depot level maintenance working with the full time small arms guys, and they just don't treat their gauges with the same reverence that you seem to suggest. It's not that the gauges are 'free', it's the fact that they're just not that fragile. The part of the gauge that's important to keep pristine is the shoulder cut at the very front. The idea that the gauge may scrape against the side of the chamber just isn't an issue because the amount of ejector spring pressure is minimal.


The depot should 100% verify the gauges on a schedule to maintain in house certification, if not send them out for certification. Any quality department does this. If they don't they are 100% wrong and will not pass any outside quality standard or audit.

I'm not talking about them. They should have training and budgets for this. The can chart wear/replacement over labor and material costs and find a good ratio that determines the best business case. Or they're just doing what's easy at greater expense with no actual idea of how to run a quality department.

End users, hobbyists, whoever, do not have a quality department. Gauges do not get verified.

I know how fragile gauges are. I'm not worried about 10 uses or 50 uses. I'm worried about my gauges falling out of spec as I use them for the rest of my life. No spring pressure to force metal on metal drag on the gauge. No requirement to overcome a 5-15lb ejector spring against the critical gauge faces. I suspect, depending on use, I will eventually send them out for verification if the cost is less than replacing the gauges for piece of mind.

Edit;
By the way, this is part of my job. I'm the engineering manager for a small manufacturing company. I run our quality program. I am responsible for all code compliance. I write the standards, train the employees, and develop the system to assure compliance.
 
Posts: 5822 | Location: Romeo, MI | Registered: January 03, 2009Reply With QuoteReport This Post
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