Same AR Bolt Multiple Rifles ~ Checking Go No Go Headspacing

[Frankly]

AR Building

 

I understand ideally you check with the specific bolt to be used but in the case of building uppers for other people and not having their bolt on hand, is it still an acceptable practice to use a bolt sans extractor/ejector to check headspace using Go/No-Go Gauges? My understanding is the variable is how you've mounted the barrel (ie not far enough in) but name-brand quality bolts should be consistent? 

 

What to companies that sell complete uppers without bolts do? 

[Chui]

What *I* would do if I were to manufacture bolts I’d make them print holding the longitudinal length to a very low tolerance.

For example, the print may call out 35mm +0.1mm/-0.15mm (I’m making this up).

I’d insure that the dimensions are nominally 35mm and the variance WITHIN what’s allowable.

In other words, QUALITY CONTROL & QUALITY ASSURANCE.

Now... what DO THEY DO?

I cannot imagine them deviating from what I’ve outlayed.

It would be interesting to measure, say, 10 examples of Colt, BCM, LMT, etc., bolts with statistical analysis.

That would make a nice technical article.


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[chicoredneck]

6 hours ago, Chui said:

What *I* would do if I were to manufacture bolts I’d make them print holding the longitudinal length to a very low tolerance.

For example, the print may call out 35mm +0.1mm/-0.15mm (I’m making this up).

I’d insure that the dimensions are nominally 35mm and the variance WITHIN what’s allowable.

In other words, QUALITY CONTROL & QUALITY ASSURANCE.

Now... what DO THEY DO?

I cannot imagine them deviating from what I’ve outlayed.

It would be interesting to measure, say, 10 examples of Colt, BCM, LMT, etc., bolts with statistical analysis.

That would make a nice technical article.


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That’s basically what they do. The problem arises with tolerance stacking. The barrel extension, barrel, bolt, and bolt carrier all have an impact on headspace and they all have an allowable tolerance level that is very small. But if you get two or more of these pets that are at have within this margin but not exact, you can start having problems with your headspace and other issues.

 

To answer the OPs question, you need to headspace it with the actual bolt that will be used in the rifle to really know %100.

[Chui]

^ Bingo!


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[dauntedfuture]

You should HS check the bolt w. the barrel.  The headspace is "set" in relation to the barrel extension, as the barrel extension retains the rear of the bolt lugs.  The barrel extension and the barrel and the bolt control headspace.  In reality, its not "how far in" you set the barrel on at into the receiver provided its at least hand tight; provided the barrel assy. is hand tight to 30 Ft lbs, the headspace would not change w. a given bolt.  

[Frankly]

I saw one video where the guy took a bolt and barrel with extension, inserted the Go-NoGo gauges and simply twisted the bolt into the barrel and either it turned or not. I'm assuming this is all they can do when they sell you a barrel with a "headspace" bolt but wouldn't a falsehood since you should check with the rifle assembled and the bolt in your BCG? 

[kurtm]

Yes and no, it will give you a go, or no go indication by hand as the lugs are radial. It will either turn or not turn. The best way is bolt in carrier, but the bolt needs to be stripped of it's extractor AND ejector! 

Folks make WAY to big a thing.out of this. If it doesn't drop primers, and or it closes on factory ammo without sticking go shoot the sh#t out of it and have fun!

[Paul-the new guy]

2 hours ago, kurtm said:

Folks make WAY to big a thing.out of this. If it doesn't drop primers, and or it closes on factory ammo without sticking go shoot the sh#t out of it and have fun!

 

This!!  At one time I had 3 uppers that I used the same bolt/BCG in.  Worked like a champ. 

[Frankly]

10 hours ago, kurtm said:

Yes and no, it will give you a go, or no go indication by hand as the lugs are radial. It will either turn or not turn. The best way is bolt in carrier, but the bolt needs to be stripped of it's extractor AND ejector! 

Folks make WAY to big a thing.out of this. If it doesn't drop primers, and or it closes on factory ammo without sticking go shoot the sh#t out of it and have fun!

 

Yeah you're right. All the same maybe I'll have my ex-wife have the first few pulls of the trigger on a new gun  

Edited March 13, 2019 by Frankly

[kurtm]

Excess headspace will NOT cause a gun to "blow up". It can be real rough on the brass, and a potential eye injurer, although not on the AR  platform. It can be hard on the brass, it can cause the primer to back out of the case, and it could cause firing pin erosion. But all that is real minor. Just put on good quality shooting glasses and blast one out, look at the case, and if it looks ok rinse and repeat 15-20,000 times!