Headspace-AR 15

[Glenn Berryhill]

Still new to the AR 15 scene but doing my best to learn.
1. If I buy a complete upper from the same company/manufacturer (well known), should I be able to expect the headspace to be correct?

2. If I buy a barrel and BCG from the same company/manufacturer, (well known), and they tell me they "will work together", should I be able to expect the headspace to be correct?

 

[Gojo03]

I would expect the headspace to be correct in both situations. Doesn't mean it will be, the only way you would know for sure is to check it yourself, however I would run both options with no extra checks

 

[Demi-human]

Ditto.
(Caveat.)
It isn’t right, and every rifle should be checked for headspace before firing.
But in reality, millions of these rifles have been put together with remedial tools, on a kitchen table, without chamber gauges.
The manufacturing tolerances are very tight, enabling interchangeable parts and inter-manufacturer comparability.

“If the headspace is wrong, what could I do about it?”, I asked once.

Short of trying many bolt heads (how different can each really be?), or removing the barrel extension and turning the barrel down like any other rifle?(On a machine lathe, with tools I don’t have, then reinstalling the extension with the gas port and barrel tab aligned.)

Nothing.

And yet, headspace is not the major problem with this type of rifle, even with the glut of novices putting together the cheapest thing they can make.

2. If I buy a barrel and BCG from the same company/manufacturer, (well known), and they tell me they "will work together", should I be able to expect the headspace to be correct?

That’s how I went about it. Were I making many .223 ARs, I’d get gauges. But the AR interests me more in every other cartridge. So I pays me money and rolls me dice. Buying better than average parts, fitting and measuring things as they are assembled, just in case.

If I put a case in the barrel and mate the bolt to it and the case slides out through the muzzle, I may need a new barrel, not a bolt...

 

[edwardware]

@Demi-human hit it. I've handled quite a few kit builds I was helping friends with, or teaching people to reload for, and not a one of them had excessive headspace. This across ~ a dozen BCA, PSA, and similar mid-grade brands.

At this point, I wouldn't bother buying the headspace gauges if you don't have some other reason to spend the money.

 

[sarduy]

The AR platform it’s almost 99% headspace correct nowadays, i have build a lot of rifles from kits of the same manufacturer and from kit that every single part is from a different brand, you should be good to go in both cases.

 

[DoubleMag]

Not to veer off course from OP. Switch lanes perhaps.

308 / AR10 same generic rules, should be Ok but could always gauge?

 

[entropy]

Still new to the AR 15 scene but doing my best to learn.
1. If I buy a complete upper from the same company/manufacturer (well known), should I be able to expect the headspace to be correct?

2. If I buy a barrel and BCG from the same company/manufacturer, (well known), and they tell me they "will work together", should I be able to expect the headspace to be correct?

99.9999999999999999% of them are. If you are concerned, you can either buy a headspace gauge (No-go gauge) or have a gunsmith check it for you.

Not to veer off course from OP. Switch lanes perhaps.

308 / AR10 same generic rules, should be Ok but could always gauge?

The AR-10's are a bit more proprietary in manufacture. Some parts from one manufacturer might not fit with another's. The barrels and bolts are the parts most likely to interchange, though. If you are putting a complete upper on a lower, then sure; building one from a box of parts (and this holds true for 5.56 AR's also) it might be a good idea to check them.

 

[Varminterror]

@Glenn Berryhill - even if you buy bolt/BCG and barrel from different manufacturers, it’s extremely likely they will combine for appropriate headspace. I’ve come across only 3 mis-fitments which I can recall in over 600 AR uppers in the last 21yrs, one bolt truly was out of spec, the others were simply a matter of tolerance stacking, and swapping bolts around brought the headspace into spec (which I appreciate a guy buying ONE bolt and ONE barrel may not be able to do).

I’d never tell a guy he shouldn’t confirm headspace, but I’d be lying if ignored my own relatively high volume experience which shows improper headspace between quality parts is exceptionally rare, almost to the point of non-occurrence.

Unless you are buying an advertised precision matched and headspace bolt and barrel, I do not believe there is ANY reason to expect buying both from one manufacturer will actually be more consistently within spec than buying from two separate manufacturers.

 

[CapnMac]

Headspace issues in AR-15 are going to be restricted to a glitch in the bolt face/bolt lugs dimension, or to chamber depth reaming. That latter is going to be restricted to not reaming deep enough, for most practical purposes.

The dimensions are extremely well known, and easy to QC gauge in factories. As noted above, thousands of these are in the field with no reported major issues. Both as complete uppers and as any variety of parts build-up uppers.

Pretty much legos, and to the point that you can use brix or duplo, too.

 

[edwardware]

Pretty much legos, and to the point that you can use brix or duplo, too.

Heresy! Burn him!

 

[Glenn Berryhill]

Thanks all. I feel more comfortable about shooting the AR 15 for the first time soon. The only AR I have had up till this point was a complete Sig M400. I also purchased a barrel and BCG for an AR 10 too. It has a way to go before I worry about shooting it. Waiting on parts unfortunately.

 

[CapnMac]

Heresy! Burn him!

LoL! I do not weigh as much as a duck. Unless it's a duck comprised of pig iron []

 

[tommy.duncan]

I do not weigh as much as a duck.

Only at THR can we get Holy Grail references in an AR15 thread!! Awesome!!

 

[CapnMac]

Only at THR

Could be quoting Tommy Duncan lyrics []

 

[d2wing]

If they are in spec it shouldn't be a problem, but I did have a PSA with an out of spec bolt and BCG. I notice that some higher grade barrel makers offer bolts matched to the barrel. In the case of the PSA, it fired and function but accuracy was horrible due to irregular lock up and maybe headspace. My guess is that I just had unusually bad luck and nearly all will be in spec and function fine. If I were match shooting I would consider measuring and possibly blueprinting as you would with a match bolt action rifle.

 

[MySuomi]

This sounds like an opportunity to gain some knowledge: I have never worried about headspacing in an AR build since I was relying on the ability of the bolt to close and latch properly. I have assumed that if the bolt will close and lock then the headspace is within spec.

Is my assumption correct? Thanks for any clarification.

 

[entropy]

It is not.

 

[MySuomi]

Entropy- Thanks that is good to know.

 

[entropy]

I suppose I should qualify that with just because the bolt closes and locks, doesn't necessarily mean the headspace is within spec. The chamber could have been reamed too long, the bolt face could be too deep, or the barrel seated too short; any of these would allow the bolt to close on round. It could cause excess pressure, especially the combination of any of the two. It would more likely cause a stuck case or a separated case.

 

[Hjalkarsson]

usually, the cause of excesive headspace is when the gun has been shot enough times that the lugs on the barrel extension stretch and the lugs on the bolt compress. for that reason, it's generally OK to use a new bolt with a new barrel. used bolt on a new barrel, or new bolt on a used barrel, you might want to check it. used bolt on a used barrel you definitely want to check it before use.

when you use a headspace gauge, you have to clean the chamber and bolt really good, and take the extractor and ejector off the bolt so there is no interference. you have to gently close the bolt on the headspace gauge, treating it like glass so it doesn't deform even 0.0001"

and then "closing" the bolt is a subjective process. sometimes it will close sort of. or start to close but not really. now what? did it "close" or not? it's a finicky process.

furthermore, a gunsmith I was working with just the other week told me the headspace gauges you get are actually generic, the different manufacturers all have their own headspace gauges for what they think is appropriate. that doesn't make sense to me because 1.4666" is 1.4666" isn't it? but they don't think so and there you are.

HOW TO USE HEADSPACE GAUGES (personal notes)

the gauges you use, should come in a set from the manufacturer. do not mix and match.
.223 and 223 Wylde use the same gauges. 5.56 NATO is slightly larger.

0. all parts must be room temperature.
1. make sure the rifle is unloaded, no magazine, no ammo in the work area.
2. take the upper receiver off of the lower receiver. remove charging handle and BCG.
3. remove the bolt fron the carrier. clean both of them.
4. remove the extractor, ejector, and firing pin from the bolt.
5. put the bolt back in the carrier. install cam pin to hold it together. do not install the firing pin.
6. clean the chamber thoroughly so there is no gunk.
7. insert the gauge into the chamber.
8. insert the BCG into the upper receiver without the charging handle.
9. slowly and carefully close the BCG onto the gauge. never apply force. treat the gauge like glass. it must not get deformed even 0.001 inch.
10. "closing" is when it moves forward completely. "locking" is when it also rotates the bolt completely to the locked position.

GO (Minimum Chamber) 1.4636" (.223, Wylde) 1.4646" (5.56 NATO)
bolt should lock closed on the gauge. (it's smaller than an actual cartridge)
if it does, headspace is less than the minimum allowed.

NO-GO (Max Chamber) 1.4666" (.223, Wylde) 1.4696" (5.56 NATO)
bolt should not lock closed on a new barrel.
may partially lock closed on a used barrel, indicating wear and not much life left.
if so, test with a field gauge.

FIELD (Reject) 1.4696" (???)
bolt should not lock closed. (it's larger than an actual cartridge)
if it does, headspace is excessive. do not use the rifle. likely to kaboom.

Colt Factory GI Reject (Absolute Maximum) 1.4736"
bolt should never close. (it's much larger than an actual cartridge)
if it does, it's a wonder it hasn't blown up already.

there is some confusion about the actual measurements of a NOGO gauge. if a manufacturer sells a set of GO and NOGO gauges, the NOGO is actually a FIELD gauge. if a manufacturer sells a set of three, GO NOGO and FIELD gauges, the NOGO is smaller and the FIELD gauge is actually the size of the NOGO gauge from the set of two.

a lot of people just use the GO and FIELD gauges, they don't bother with the NOGO gauge.
or, a lot of people use the NOGO gauge and don't bother with the other two.
some think that as long as it chambers a round, a GO gauge is unnecessary.
some put a piece of tape on the base of a GO gauge and use that as a NOGO gauge.
a FIELD gauge is a must-have, to test used and worn rifles. but, rifles rarely fail that test.

each barrel manufacturer has their own set of headspace gauges, to their own precise specifications, that they use at the factory, and they are all different. the ones that you buy (Clymer, etc) are actually "generic" headspace gauges, which will then reflect some variation between manufacturers.

 

[entropy]

there is some confusion about the actual measurements of a NOGO gauge. if a manufacturer sells a set of GO and NOGO gauges, the NOGO is actually a FIELD gauge. if a manufacturer sells a set of three, GO NOGO and FIELD gauges, the NOGO is smaller and the FIELD gauge is actually the size of the NOGO gauge from the set of two.

Incorrect. You are relying on hearsay.

furthermore, a gunsmith I was working with just the other week told me

GO is GO, NO GO is NO GO, FIELD is a military designation for a looser NO GO; the only reason they are sold commercially is for milsurps. FIELD should only be used on milsurps or military rifles, not commercial guns, and NO GO is the standard for commercial guns. If a commercial gun fails NO GO, it should be repaired if possible or retired if not. If a milsurp or issue rifle fails NO GO, you check it with the FIELD. It is still fireable if it passes FIELD, though it is an indication that it should undergo a major refurb when possible. (Hence the FIELD designation; during action, a rifle couldn't conveniently dropped off at the Depot for a refurb. The soldier would have to continue to use it until such time (rotation out of the FEBA, ETS, etc.) that it could be serviced.

Can you tell us which gauge manufacturers engage in this chicanery so I can avoid them in the future?

Colt did make very loose FIELD gauges because of the early problems with M16's jamming, prior to the issue of the M16A1. I should think they've retired them by now. The ones I had weren't to your 1.4736" spec , anyway.

I helped Okie test his headspace gauges for 7.62x54R and .303 British when he first started selling them, and did extensive measuring of them during testing. We used the original military values for each set.

each barrel manufacturer has their own set of headspace gauges, to their own precise specifications, that they use at the factory, and they are all different.

I guess we're all screwed then, because the manufacturers don't sell their gauges, and two, I guess they don't need to keep to SAAMI specs if their gauges are significantly different.

I did prefer the headspace gauges we had in the Army, they are the gold standard for 5.56. I've only used the Clymer in .223, never had a commercial rifle fail NO GO; I had several M16A1's fail Field. Fortunately, my SMOS was 45B, so I could do the work myself instead of turn them in and wait.

 

[Hjalkarsson]

those were my personal notes as to the best understanding I could get. if something is wrong I would like to get it straightened out, because the purpose is to have the correct working knowledge.

no, I don't have an indication which gauge manufacturers fudge the description of their gauges. I don't have a reference as to where that came from or I would post it. I assure you it came from a reputable source or I wouldn't have glommed that bit of info.

the part about manufacturers using their own gauges (therefore specs) and they're all different, that's what the gunsmith told me, and he is definitely reputable. I won't say who it was because this doesn't need to go that far and he doesn't need to get dragged into it. but, I know him, and quite frankly I don't know anything about you, so I'll defer to what he said.

 

[entropy]

76Y10 MOS, 45B 20 SMOS. If that means nothing to you, If have to explain, you wouldn't understand.

 

[12Bravo20]

76Y10 MOS, 45B 20 SMOS. If that means nothing to you, If have to explain, you wouldn't understand.

And there was time the 45B's would bring stuff to me to work on (44E) instead of sending it to depot

 

[Glenn Berryhill]

Are y'all speaking in tongue?