AR15 Headspace Go - Fail

[jman841]

So I just built a new AR-15 using a Criterion barrel and an Aero Precision Bolt Carrier Group. It is chambered in .223 Wylde.

I also purchased some go, no-go gauges jsut to be safe as I also did a barrel change on my old AR-15.

I did a quick check of the go and no go gauges and the old bolt carrier group I have passes without any issue on both rifles, but the new Aero Precision bolt carrier group I have fails the go gauge (It will no close) on both rifles.

I did not remove the extractor and ejector for this test, but I typically do a quick test first by guiding the gauge into the chamber before removing it.

Is there any reason why it would fail the go gauge (1.4636 min gauge) on that bolt only?

This is a 5.56 nato min gauge and the chamber is .223 wylde, but from my understanding, it should pass the 5.56 nato gauge without issue, and it does with my other bolt.

[Shadow9mm]

5.56 nato has a LOT longer throat. wylde has a throat similar to 223, but the angle is cut differently to allow 5.56 use, is my understanding. check out school of the american rifle on youtube. they have some amazing videos showing use of several different, go, nogo, and field gauges and how to use them while inspecting rifles.

[stagpanther]

switch the bolts in the carriers and see if the same problem persists. Who's gauges are you using? Also, take a cartridge case (doesn't matter whether it's .223/5.56 or wylde since the headspace is only affected by the shoulder datum and bolt dimensions) and see if the bolt will close on it. Mic the aero bolt and see if the bolt face depth and lug dimensions are in spec (sorry, I don't remember them off the top of my head but a little net searching should reveal them).

I assume your chamber is completely clean and free of debris--a piece of debris lodged on the shoulder might be enough to cause a problem.

Often a new BCG will offer quite a bit of resistance to closing and locking up with the extension--especially if you haven't removed the ejector and extractor.

Another thing i would check with the aero bcg--without messing with anything else, no gauges etc, and the upper separate from the lower, simply press the carrier to close the bolt on the barrel's extension. The bolt engagement and rotation should be easy and fairly low resistance. Also, the back of the carrier should be flush with the back of the upper receiver with the bolt closed to the extension.

[4V50 Gary]

You should remove the extractor and ejector before checking headspace. Then get back to us.

[xtriggerman]

I second the removal of both extractor & ejector for the most accurate read when this sort of thing comes up. I think a go gauge is going to tell you, you have about a .004 headspace on a live round. If every thing as far as the metal finish is good with no bur anomalies, You might be just under that minimum head space with like 2 or 3 thousandths behind a live round. Using a stripped bolt head, get a couple of each different live rounds that you may have and try to put them in battery with the stripped head. If you get drag on a live round, send the barrel back. if you get no drag turning the bolt head into battery and feel a tiny bit of loossness, your good. That senerio would put you just below the minimum head space that the go gauge is capable of. If that upper is a target play gun, low head space is even better (preferred). If its a SHTF upper, send it back if in fact the go doesent go in the final checking. JMO

[jman841]

Sorry for the delay,

So the gauges work perfect on my old bolt and bolt carrier group (It's a Delton BCG that I've had for years). It passes both the no go and the go gauge.

There is significant resistance trying to chamber a live round with the upper removed by pressing the round in by hand with the Aero Precision BCG, with the delton, it's a little bit of finger pressure and slides right in like I am used to.

Aero Precision has offered to confirm headspacing, I will send my barrel to them with the bolt carrier group and they will confirm.

The gauges are Forster and aero precision is claiming those gauges are notoriously inaccurate.

I'll try using the other bolt with the aero bolt carrier and see how that feels, but it does not seem to be a barrel issue as my delton BCG works perfect with both barrels.

Both barrels are brand new with no round through them yet, so no issue with debris

[jman841]

Just to give some perspective on this, here's a quick video, not using a gauge but a live round. Is this normal with a new BCG? Seems to be WAY too tight in my opinion. The gauge is impossible to close and I HIGHLY doubt that removing the extractor and ejector will change anything given how hard it is to close on a live round.

https://www.youtube.com/watch?v=m-u0...ature=youtu.be

[stagpanther]

After watching that video--without the charging handle--how did you get the bolt to unlock? Did you switch the bolts between the carriers to isolate whether or not it was the carrier or the bolt like I suggested earlier?

[4V50 Gary]

First, be careful with YouTube videos. If he wants to use live rounds, that's his business. We were taught to have dummy rounds for that type of testing and to keep live ammunition away from our workplaces. If he used a charging handle, he'd have an easier time.

I cannot recommend that video except to learn what not to do.

If you're not going to headspace it right with the extractor and ejector removed, why bother trying it yourself? Glad you decided to send it off.

[jman841]

Originally Posted by stagpanther

After watching that video--without the charging handle--how did you get the bolt to unlock? Did you switch the bolts between the carriers to isolate whether or not it was the carrier or the bolt like I suggested earlier?

Yes, tried it with the other Bolt Carrier, same issue. Also put the delton bolt in the Aero Precision bolt carrier and it worked perfect.

[jman841]

Originally Posted by 4V50 Gary

First, be careful with YouTube videos. If he wants to use live rounds, that's his business. We were taught to have dummy rounds for that type of testing and to keep live ammunition away from our workplaces. If he used a charging handle, he'd have an easier time.

I cannot recommend that video except to learn what not to do.

If you're not going to headspace it right with the extractor and ejector removed, why bother trying it yourself? Glad you decided to send it off.

The reason I used a live, unfired round was due to the claim that the gauge is off. Aero Precision was saying the gauge itself is not reliable, yet you can clearly see even a live round is not allowing for proper closing of the bolt.

The weapon was pointed in a safe direction the entire time and there is no hammer connected to the weapon. I'm not sure how it would be possible to discharge given this scenario to justify your comments.

Again, the reason I used a live round as opposed to the gauge is due to the claim from Aero Precision that forster gauges can not be trusted. I do not have any .223 dummy rounds on hand. A fire case would not be a good option either as the brass would be stretched.

I don't really see how it would be possible for the round to go off or to be a safety issue, which is why I did the test.

[243winxb]

https://criterionbarrels.com/media/h...v=00dc5da36527

Matching barrel & bolt.

[tangolima]

Your rifle has short chamber that fails the no-go gauge, and the live round confirmed that. The next step is to fix it. Sending it back to the manufacturer is the best way.

-TL

Sent from my SM-N960U using Tapatalk

[stagpanther]

Also put the delton bolt in the Aero Precision bolt carrier and it worked perfect.

OK--that means your problem is almost certainly with the with the aero bolt. At this point my guess is that the problem probably lies with one of two things. The easiest thing would be to simply return the carrier group for a new one.

Measure the depth of the bolt breech face from the front edge of the lugs, as well as the depth of the lugs from front to back. I'm guessing your Delton bolt has either slightly greater depth to the bolt breech face or the bolt lugs are not quite as deep compared to those measurements on the aero bolt. It's also possible the bolt lugs may be hanging up when turning to lock to the extension, once in a while very sharp edges can do that--especially if something is slightly out of alignment.

[jman841]

Originally Posted by tangolima

Your rifle has short chamber that fails the no-go gauge, and the live round confirmed that. The next step is to fix it. Sending it back to the manufacturer is the best way.

-TL

Sent from my SM-N960U using Tapatalk

The issue is the Aero Precision bolt.

The aero precision bolt has the same problem with another barrel I have that is also brand new (Tribe Defense).

Both barrels have no issue with the Del-ton bolt I have.

[jman841]

Originally Posted by stagpanther

OK--that means your problem is almost certainly with the with the aero bolt. At this point my guess is that the problem probably lies with one of two things. The easiest thing would be to simply return the carrier group for a new one.

Measure the depth of the bolt breech face from the front edge of the lugs, as well as the depth of the lugs from front to back. I'm guessing your Delton bolt has either slightly greater depth to the bolt breech face or the bolt lugs are not quite as deep compared to those measurements on the aero bolt. It's also possible the bolt lugs may be hanging up when turning to lock to the extension, once in a while very sharp edges can do that--especially if something is slightly out of alignment.

That's a good idea, I'll measure it compared with the delton bolt.

Aero Precision has authorized me to send it back to them along with the barrel. I'll strip the barrel from the upper receiver and send them both for confirmation.

Out of curiosity, what is the danger of a tight headspace?

Since an AR-15 can't fire out of battery and the barrel won't allow the cartridge to extend too deep into the throat. Is there any risk of problems with a tight chamber lock up?

[tangolima]

Originally Posted by jman841

The issue is the Aero Precision bolt.

The aero precision bolt has the same problem with another barrel I have that is also brand new (Tribe Defense).

Both barrels have no issue with the Del-ton bolt I have.

Ah, didn't catch this part. Do you have to use this aero precision bolt? Have you tried more other bolts to be sure only this particular aero bolt causes problem?

If this particular bolt causes the issue, and you have other bolt to use, I'd rather leave the barrel alone. The barrel and bolt combination define the chamber. When you send in the barrel with the aero bolt, the manufacturer will ream the barrel to open up headspace. Now you probably will have excessive headspace when you put in other bolts. It is easier to remove than to add metal.

With short chamber (failing go), you may not be able to chamber a standard (factory) round, like you have experienced with your factory round. Not much problem if you reload. But big problem if you need a rifle that can take any factory ammunition.

-TL

Sent from my SM-N960U using Tapatalk

[4V50 Gary]

Check your gauges against a micrometer (diameter) and caliper (length). Ruger Armourer School taught us that as they check their guages that they buy.

[stagpanther]

Out of curiosity, what is the danger of a tight headspace?

If the cartridge won't go into battery, then your gun more than likely won't go bang. If I had to guess, Aero probably wants to see the chamber and extension of your barrel if they asked you to send it along with the bolt--and then will match and headspace it with a bolt. That's a mark of excellent CS in my book.