Too Little Headspace?

P

Phil3

Guest
While this question pertains to an AR15 and not a benchrest rifle, I know people here are quite qualified to speak to this topic.

I am finishing assembling my AR15 rifle and it appears it might have too little headspace. Am I right to understand that the bolt should close "easily" with the GO gauge installed? In the case of the AR, I removed the ejector, and reassembled the bolt. I fitted a Forster GO gauge into the end of the bolt (held by extractor), and pushed the bolt forward. The bolt lugs slide past barrel lugs and rotate behind those lugs to achieve lockup. The bolt, when pushed forward with single finger pressure achieves 40 - 50% lockup. Using firm two finger pressure permits 100% lockup. Is this OK?

The bolt is a Young Manufacturing National Match chrome bolt and the barrel is from Krieger with barrel extension (lugs on barrel) installed by them. The barrel is chambered for .223 Remington (not 5.56). The gauge is a Forster GO gauge marked for .223 Remington and shows a dimension of 1.4636".

- Phil
 
hmmmmmmmmmmmmm.
you say the bolt rotates with the go gage in place......that is "go".....

if the bolt lugs rotate behind the bbl extention lugs....that is "go"

what do you mean by "lock up "........if you can push the bolt forward from this position , with the gage in place, it would mean you have some clearance from the zero of "go "....
what happens with a no go ??

mike in co
 
While I agree with Mike, I want to pass on that the use of a chrome bolt is bad medicine. The military back in the late 1960 ban the use of chrome bolts. The reason was because of hydrogen enbritlement. That is why you do not see them on current issue AR's. Bolts need to have the firing pin removed before you check for headspace. The bolt locking pin still needs to be in place, so you are sure the bolt has gone forward enough to lock into the uppers cam.:D
 
mike in co said:
hmmmmmmmmmmmmm.
you say the bolt rotates with the go gage in place......that is "go".....

if the bolt lugs rotate behind the bbl extention lugs....that is "go"

what do you mean by "lock up "........if you can push the bolt forward from this position , with the gage in place, it would mean you have some clearance from the zero of "go "....
what happens with a no go ??

mike in co
Click to expand...

"Lock-up" meaning 100% turn of bolt and bolt lugs behind barrel lugs. It is possible to achieve this condition with a GO gauge, but it does take some effort (pushing pretty firmly on the bolt) to do it. I had understood this should be doable with light pressure. It is harder to close the bolt with the gauge in than without, which would seem to indicate no clearance at all.

It is impossible to even begin to close the bolt on the NO-GO gauge.

- Phil
 
Big Al said:
While I agree with Mike, I want to pass on that the use of a chrome bolt is bad medicine. The military back in the late 1960 ban the use of chrome bolts. The reason was because of hydrogen enbritlement. That is why you do not see them on current issue AR's. Bolts need to have the firing pin removed before you check for headspace. The bolt locking pin still needs to be in place, so you are sure the bolt has gone forward enough to lock into the uppers cam.:D
Click to expand...

As best as I can find, hydrogen embrittlement issue is not longer much of an issue, but I am no expert on this. I don't understand why the firing pin has to be removed. It does not protrude from the bolt face when the bolt is locked. The hammer will drive it forward, but it does not rest in a protruding position. Also, the headspace gauge has a hole for the firing pin.

I thought perhaps the chrome plating may cause a problem due to thickness, but Young says the plating is .0002" thick and emphasized it is NOT .002". Krieger, the barrel maker said their barrels are not made so tight where .0002" would make any difference.

- Phil
 
as this is not a "bolt" gun in the normal sense of a hand operated bolt, there should be NO resistance to the bolt turning into place. bbl with bbl extention, stripped bolt and the go gage.
if it works you should go on to check inserted in the carrier, for function, but not with the gage.
and while we are on the subject , the term "national match" is a marketing term for the ar market. there were match 03's and match garands, match m14's built to spec's by the military for competiton, not for the m16...never. the military built match m16 have basically used commercial parts, not custom mil match parts. chrome has a significant thickness and the raw manufactured bolts would have to be built "under" normal spec to make up for the build up. seems unlikely.
mike in co
 
Last edited by a moderator:
Mike,

Thanks for your reply.

There is no practical way to check headspace without using the entire bolt and carrier assembly. When closing the bolt assembly, lugs slide past and behind the barrel lugs, and movement is also happening within the bolt assembly itself. These things provide some resistance, and can not see how the bolt assembly, even if stripped, would lock into place, say under its own weight. Maybe it should, but mine is stiffer than that. Even with no gauge or round in the chamber, there is resistance felt.

I mentioned National Match strictly as a model identifier, not as something that makes it special, though this one has some features apart from Young's other chrome bolts. I know "National Match" is thrown around loosely, but thanks for the history on when it actually meant something.

I spoke to Young about the chrome plating thickness. They said it is .0002" thick, and emphasized, repeatedly, that it is NOT .002". I called Krieger, the barrel maker and asked if .0002" would make a difference on headspace. They said their chambers are cut so that an additional .0002" thickness on the bolt, would not be enough to cause a problem. Later on, I recognized that the .0002" is on the bolt face and the back of the lugs, shrinking headspace by .0004". A problem? I don't know...maybe I am seeing it here.

I loaded a live round, and the bolt appears to close normally. Hard to say, because you can't see anything to know.

- Phil
 
If you gauge some factory loaded ammo and compare those measurements with that of your GO gauge you will probably stop worrying. For chores such as this, I like the caliper attachment that Stoney Point came up with, and is now sold by Hornady. If you are reloading for a semi-auto, I presume that you know that more shoulder bump (than is the usual for bolt rifles) is in order.
 
Boyd Allen said:
If you gauge some factory loaded ammo and compare those measurements with that of your GO gauge you will probably stop worrying. For chores such as this, I like the caliper attachment that Stoney Point came up with, and is now sold by Hornady. If you are reloading for a semi-auto, I presume that you know that more shoulder bump (than is the usual for bolt rifles) is in order.
Click to expand...

I pulled the extractor (and ejector) and tried this test again. To my surprise, it now closes easily on the GO gauge, but absolutely will not on the NO-GO gauge. Excellent! The extractor certainly DOES make a difference. Another firearms lesson learned.

I will reload and am learning more about optimal case resizing, shoulder bumping, etc. but yes, recognize what you say as something I need to be mindful of when reloading for semi-autos.

I will probably order the Stoney Point tool.

Thank you.

- Phil
 
Phil3 said:
There is no practical way to check headspace without using the entire bolt and carrier assembly. - Phil
Click to expand...

phil,
why ???
bbl with bbl extention installed, stripped bolt and the go gage is all you should have when checking headspace on an ar bbl.....no upper, no lower, nothing else. either you can turn the bolt or you cannot. this is about chamber headspace, not how the upper, lower, carrier operate. those should all be check seperate from checking headspace.

it sounds like make you got there.

mike in co
 
mike in co said:
phil,
why ???
bbl with bbl extention installed, stripped bolt and the go gage is all you should have when checking headspace on an ar bbl.....no upper, no lower, nothing else. either you can turn the bolt or you cannot. this is about chamber headspace, not how the upper, lower, carrier operate. those should all be check seperate from checking headspace.

it sounds like make you got there.

mike in co
Click to expand...

The barrel, receiver, handguard, gas tube, gas block are all together. I see what you mean, if they were not. Just just the stripped bolt (no carrier needed), the gauge, and the barrel w/extension. Most definitely will do it that way next time! I was following the AR 15 videos on Brownells.

Thanks.

- Phil
 
any data arrived at with the assembly vs the stripped parts is questionable. the good news is it will not close on the go no gage. honestly if you are worried about the fit of the seperate bolt( as in not furnished with the bbl assembly), you should remove the bbl from the other parts, and check.

ar's are built to spec. the good news is i have to recd any out of spec parts, and all of my guns have gone to gether in spec.

mike in co
 
Phil
I have never owned or shot an AR but I have owned and shoot alot of Browning BAR's and in all of them you really need to let the bolt slam home to get the rifles to even fire.You can't close them gently.
Lynn aka Waterboy
 
lynn,
i dont disagree.
but
checking headspace and checking operation are two different tasks.
bbl, stripped bolt, lugs( either reciever.or bbl extention in the ar case) and the go/no -go gages are all you need to check headspace.

mike in co
 
I wouldn't even fart around with the Go and NoGo gauges. They are basically irrelevant to your situation.

Failure to fire is a diagnostic for short headspace.

Take about 3 or 4 cases sized in YOUR sizing die and seat bullets to 2.25". Insert these into a magazine and cycle by hand. If you get a couple that the action won't completely lock up on, pull the bolt all the way back and let fly on them. If they chamber then, you are good to go. Headspace will loosen up a maybe a thou as the chamber is polished by cases feeding.
If none of the cases will allow the action to lock, you will need a finish reamer from a shorter-throated chamber style. Give it just the lightest twist in the chamber - you don't want to overdo it. Usually just the lightest chips are all you need.

Long headspace

Use a Stoney Point headspace gauge or similar tool to compare fired cases to your resized cases. They shouldn't be more than about .005" longer in headspace length than your sized cases. If they are, adjust your die out longer. I like fired cases to be about .003" longer than sized cases.
If you can't adjust your die to achieve that, try another die or get rid of the barrel.

All that said, I think your barrel is fine.
 
glad to see a gunsmith jump in and give the correct process to check what the customer asked
what a joke.

he never once said anything about function of his rifle...he has not fired it yet based on his other post on the scraches in the muzzle.
he asked about headspace and in reference to headsapce gages and his chromed bolt

consider reading and answering the question asked..


mike in co
 
What I have done for the past ten+ years on every single bolt action/AR style semi auto I have built using a rimless centerfire cartridge.

Get a spool of .001" thick shim stock from Starrett.

Cut several pieces with sharp scissors that will fit inside the face of the bolt.
Place your GO gauge into the chamber and attempt to close the bolt using no shim stock. It should go into battery with using nothing more powerful than gravity. (completely strip ALL peripheral components from the bolt, bolt carrier, etc. No pins, no extractors, no springs. fundamental components only)

Now remove the bolt and insert a single piece of shim stock. Use a little dab of sticky grease to keep it in place.

Reinstall the bolt. Ideal world on a gun is that the bolt will refuse to rotate into battery.

So, if this were the case, your headspace can be referred to from this point forward as "GO +.001".

Here is why this is kinda cool. It's .006" from GO to NOGO in almost all cartridges according to SAAMI. Using this procedure means the NOGO gauge becomes all but unnecessary.

So, if a guys "Ackley, neckturned, 600 Nitro", 1500 mile maximum bad ass Pro Stock, bench gun is initially set up at GO+.001" and after 500 rounds its GO+.007" he knows that something moved and he knows exactly how far and how many rounds it took. (assuming the same GO gauge is used during the evaluation)

While this may be viewed as a bit obsessive it has proven useful to me over time. I can quickly determine if a customer has been abusing a rifle by loading his cartridges like he's running a Top Fuel car. Or if the material yielded due to a poor heat treat.

Just another way to peel skin from cats.


Cheers and all the best,


Chad Dixon
Gunmaker
LongRifles, Inc.
 
Mike In Co
I was trying to let Phil no that you need to let things fly on a complete rifle.In his post he said the extractor and everything else was all put together.In that configuration if he just slides the bolt closed chances are it won't close on his go gage.If he lets it fly it will probaly close without issue.He can then try his no go gage in the same manner and prove to himself all is right.
He bought all of the pieces from a reputable source so I doubt anything is out of whack.
If he is the Phil I think he is we are shooting a 1,000 yard match on the 4th sunday of september at the sacramento club.If he comes out he can shoot my heavygun while I'll dial in the tuner settings in preparation for the big match in october.Should be able to shoot 1 amazingly small group out of the 3 targets.
Lynn aka Waterboy
 
The Extractor & Ejector Must be Removed.

I pulled the extractor (and ejector) and tried this test again. To my surprise, it now closes easily on the GO gauge, but absolutely will not on the NO-GO gauge. Excellent! The extractor certainly DOES make a difference. Another firearms lesson learned.
Click to expand...
The instructions state this, and you are not to slam the bolt on the gauge. :)
 
243winxb said:
The instructions state this, and you are not to slam the bolt on the gauge. :)
Click to expand...

If you read my post I said the gun was not dis-assembled and it won't work without slamming on a assembled gun.
The instructions are written so you don't chip the gage.
Waterboy
 
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