AR15 headspace measurement

[freebird]

I've always removed the ejector before measuring AR15 headspace. Having done this a total of about 4 times, I have a question about measuring headspace with the ejector installed.

If measuring headspace with the ejector (and spring) installed do you:
- get false fails (I'd be ok with this, unless it always gives a false fail)
- get false passes (not good)
- or basically, it's more of a PIA than just removing the ejector?

Thanks.

 

[outrider58]

Can't have pressure on the gauge I wouldn't think. I pull the ejector using the press.

 

[K-43]

What outrider said. Same with any spring loaded plunger gun. The Gauge has to be free to move or you can't feel the actual resistance. You're supposed to push and turn the bolt by hand lightly so you feel the resistance and don't damage the gauge or chamber.
The pressure of an ejector might just be strong enough to say you're bolt isn't closing, when in fact it's the ejector pressure. People will say they do it. And they do. But the gauge manufacturers made the no ejector/no extractor rule.

 

[freebird]

The ejector spring is 'only' around 8lbs. I'm still struggling to understand how/if that would change the results, and if it does, would it change them to show false passes. Let's assume barrel is not installed, which makes the test quite a bit easier.

All that said, I could NOT remove the roll pin in a recently purchased toolcraft bolt. I think my problem is my roll-pin punch set doesn't have the perfect size for this pin. One punch is ~2mm diam,and is too big, and the other is around 1.7mm and seems to easily slip into the ID of the pin. Makes it a PIA to remove the pin.

What roll pin punch are you guys using for this?

 

[BradMacc82]

I have a 1/16" punch that I shaved down some for popping the roll pin out.


*Can't recall which size allen key, but I've also been able to pop that roll pin out using one of those and a small 'smith hammer.

 

[freebird]

^ that's a good idea. Thanks.

 

[BradMacc82]

Creative problem solving, name of the game at times.

 

[Doco Overboard]

The ejector spring is 'only' around 8lbs. I'm still struggling to understand how/if that would change the results, and if it does, would it change them to show false passes. Let's assume barrel is not installed, which makes the test quite a bit easier.

All that said, I could NOT remove the roll pin in a recently purchased toolcraft bolt. I think my problem is my roll-pin punch set doesn't have the perfect size for this pin. One punch is ~2mm diam,and is too big, and the other is around 1.7mm and seems to easily slip into the ID of the pin. Makes it a PIA to remove the pin.

What roll pin punch are you guys using for this?

The plunger could side load the gauge and on a chamber with an excess radial dimension could read differently.
Not to mention having a spring loaded plunger is hard to overcome the light touch needed to prevent unnecessary damage. The gauges are hardened and barrel steel is soft.
M1917's are notorious for not being gauged correctly. And they have a standing ejector. Once you feel resistance stop, or you can swage the chamber gauging surfaces or ruin an expensive gauge.
Manufacturing tolerances can make the problem worse.
Head-space means the longest cartridge will fit the shortest chamber and the shortest cartridge will contact the gauging surface sufficiently to make sure there is no dangerous slack to the bolt face. The gauge needs to bear against the gauging surface (s) not the ejector.
There were gauges for sale here that were sufficiently ground in the ejector area to eliminate the headache of pushing pins in and out. Beware of doing it yourself because you can ruin the heat treat if you get the gauge too hot.

 

[outrider58]

^ that's a good idea. Thanks.

If you own an AR 15 or two, you owe it to yourself to buy a set of roll pin punches. You will get plenty of use out of them.

https://www.ebay.com/itm/9pc-ROLL-P...343208?hash=item33b532e368:g:xngAAOSw-RRXDD7F

 

[freebird]

If you own an AR 15 or two, you owe it to yourself to buy a set of roll pin punches. You will get plenty of use out of them.

https://www.ebay.com/itm/9pc-ROLL-P...343208?hash=item33b532e368:g:xngAAOSw-RRXDD7F

I own a set of roll pin punches ("Grace USA", if that is worth anything https://www.amazon.com/gp/product/B007WADKN0 ).

BUT, that bolt roll pin size falls between the sizes I have.

 

[outrider58]

I own a set of roll pin punches ("Grace USA", if that is worth anything https://www.amazon.com/gp/product/B007WADKN0 ).

BUT, that bolt roll pin size falls between the sizes I have.

They do make that size pin punch. My set(not necessarily the one I quoted you) came with one.

 

[BradMacc82]

FWIW, the allen key trick - that size (using calibers, cause I can't find the part with the stamped size) is 1.25mm or .050".

 

[K-43]

FWIW, the allen key trick - that size (using calibers, cause I can't find the part with the stamped size) is 1.25mm or .050".

I've been guilty of that. So Bubba.

 

[BradMacc82]

It ain't Bubba if it works.

May not be the ideal tool for the job, but the fit is almost ideal - I haven't peened/split a single ejector roll-pin using that trick, so far.

 

[clandestine]

Yes, you need to remove the ejector to get a proper reading. Or you need to have gauges that are modified to work with the ejector and extractor installed.

The Ejector Weight on a good spring varies from 8-10#.

The TM states that it is permissable to use 8.5-8.75 # trigger weights on the tail of the carrier to check for HS checks, you can see where this would be a problem when the Ejector won't collapse till 10#.

 

[clandestine]

If the pin won't come out, then it should come out. The pin is corroded or sheared and will lead to problems.

Ideally you need 3 size 1/16" punches to remove stubborn ejector pins. A long 1/16" roll pin Punch, a medium length 1/16 (cut down and no ball tip), and a stubby with no ball tip that is cut down so you only have about 1/4" of the skinny section of the punch left.

Using roll pin punches to drive out pins can make them mushroom and very difficult to remove. Roll pin punches should only be used to do a final set of the roll pin to seat in in it's bore.

If the pin is stuck some kroil oil helps at times.

 

[freebird]

Thanks Clandestine, excellent info. Much appreciated!