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Old August 23, 2015, 02:33 AM   #1
Renegade19sc
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Headspace in rifle

I have a rifle that will close on a No Go gauge. I have taken some fired brass from the rifle and measured it in a RCBS mic along with the no go gauge. Two out of three pieces of brass are almost equal to the no go gauge and the third one is a thousands greater. My question is roughly how many rounds would a rifle have to go thru before the headspace is closer to a field gauge which is 4 one thousands greater than the no go gauge. This may not be a question that can be answered but I wanted the opinion of the experts as to weather or not to fix the gun to where it will not close on the no go gauge or leave it. The gun is shooting very accurate no problems on that. The rifle is a 308 win and it is a new gun probably 40 rounds fired so far.

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Old August 23, 2015, 03:25 AM   #2
firewrench044
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Too many variables to predict
old barrel ( lower grade of steel )( softer)
caliber, dirty rounds ( will wear a chamber )
I have seen new barrels that measure that way ( cheep barrel )
Try a new bolt it may just do the trick, and if not use it when you do replace the barrel
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Old August 23, 2015, 07:40 AM   #3
F. Guffey
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Quote:
to fix the gun where it will not close on the no go gauge or leave it. The gun is shooting very accurate no problems on that.
No clue what rifle we are talking about. No way of knowing how the rifle got the long chamber. My opinion? If the rifle was accurate I would apply the leaver policy, I would leaver the way I founder. I have a 98 year old rifle that has a chamber that is .002" longer than a field reject gage from the shoulder to the bolt face. That would be .016", because this stuff does not drive me to the curb I off set the length of the chamber with a longer case.

Length of case, my cases do not have head space and they have two lengths, one from the end of the neck to the case head, the other from the datum/shoulder to the case head. To form cases for the long chamber I use 280 Remington cases because the 280 Remington is .051" longer from the shoulder to the case head than the 30/06 when measured from the shoulder to the case head. My simple fix is to adjust the die off the shell holder .014" then size a 280 Remington to 30/06. I have a 30/06 forming die, that gives me two choices.

the 98 year old rifle with the long chamber is not rare. A famous gun smith was blamed for the long chambers by snarky smiths that did not understand what he was going. Back then they did not know how the rifles got the long chambers and the length of the chamber was not part of the specifications.

With the go-gage and the no go-gage the rifle chamber can pass with a chamber that is .008" longer than a minimum length/full length sized case. I am not the fan of the go type gages, I use them as transfers and standards. I measure chamber length in thousandths.

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Old August 23, 2015, 08:51 AM   #4
mehavey
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Quote:
how many rounds would a rifle have to go thru before
the headspace is closer to a field gauge which is 0.004"
greater ?
No telling (and in all probability the chamber's headspace
is not a linear function of normal-pressure rounds-fired in
a normal receiver/bolt assembly).

If you ARE a reloader, do not full-length resize, but rather
size the case only enough to fit the chamber.

If you are NOT a reloader, commercial ammo is still safe.

Last edited by mehavey; August 23, 2015 at 09:58 AM.
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Old August 23, 2015, 10:17 AM   #5
F. Guffey
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No telling (and in all probability the chamber's headspace
is not a linear function of normal-pressure rounds-fired in
a normal receiver/bolt assembly).
"and in all probability"? There is no probability. The pressure will be less. Then there is that saying: The firing pin drives the case, powder and bullet to the front of the chamber before the bang. And then? Nothing trumps a cute little saying.

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Old August 23, 2015, 10:59 AM   #6
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I have a Savage model 10 that when new would not close on a NO-GO gage . 2800rds later and I can force the bolt closed on a NO-GO gage . I'm no gun smith but assume that's normal wear on the lugs and area they lock into . I do reload and in fact have seen the measurement grow over time . I first sized my cases to 1.618 to bump .002 but now I'm sizing 1.621 to bump the same amount ( that's my comparator measurements not actual lengths ) . I've also seen some movement in my most used AR but they tend to be harder to track for me .

Based on MY rifle you have about 3K rounds to go before it starts failing the Field gage . If true that would suck because in general the 308 should do 5k easy .
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Old August 23, 2015, 11:15 AM   #7
F. Guffey
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Quote:
The rifle is a 308 win and it is a new gun probably 40 rounds fired so far.
Quote:
I have a rifle that will close on a No Go gauge.
Again, I have a rifle that will allow the bolt to close on a field reject length gage with .002" clearance. Not a problem, I use cases that are long from the shoulder to the case head, I also form 308 W cases from 30/06 cases. When forming to fit there is no way I can miss when off setting the length of the chamber with the length of the case. Again, I have two lengths, I have a length from the shoulder to the case head and I have a length from the end of the neck to the case head.

When forming 30/06 to 308 W remember the case body of the 30/06 becomes part of the shoulder and neck of the 308 W case. meaning the neck 'COULD' require neck reaming or neck turning. When forming 308 W cases for special chambers/military type chambers I find the thick neck off sets the generous chamber necks.

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Old August 23, 2015, 01:31 PM   #8
mehavey
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Quote:
Originally Posted by Guffy
Nothing trumps a cute little saying
You wouldn't mind translating would you?

As to "in all probability..." that presumes the receiver and bolt have been manufactured/heat-treated normally (and are therefore not soft), and not fed a diet of extremely high-pressure rounds where the receiver was stretched and/or the bolt set back.

For the OP's purposes/in plain English: Normally manufactured firearms don't significanylu grow in headspace beyond that of normal barrel life -- wherein you have to reset the headspace anyway when replacing the barrel.

METAL_GOD: I have to admit that I've never had a receiver stretch as you describe where it exceeded a coupla thousandths over a throat/barrel's life.

GUFFEY: I'm still working on "...the pressure will be less." Could you elaborate ?

Last edited by mehavey; August 23, 2015 at 01:36 PM.
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Old August 23, 2015, 01:43 PM   #9
F. Guffey
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GUFFEY: I'm still working on "...the pressure will be less." Could you elaborate ?
I did, you made an assumption, and I know better than to argue with someone that appears to be widely indignant about everything I post. I will wait for one of your good buddies to chime in.

It goes back to the 'factors'.

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Old August 23, 2015, 01:47 PM   #10
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Mehavey:

I'd say you're about right in regards to how much mine has changed . If I were to put a number on it I'd say the head space has grown .0015 to .002 and the rest of that difference has been my comparator insert working in from a pretty sharp square edge to that edge now having a slight radius .
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Old August 23, 2015, 01:51 PM   #11
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What you need is a Field gauge. If the bolt closes on it, the rifle is unsafe to shoot, period. A 'Field' headspace gauge can be found at Brownell's. $29.
"...I can force the bolt closed..." No force. The rifle is close to being bad, but no force is required or desired.
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Old August 23, 2015, 01:52 PM   #12
F. Guffey
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Quote:
Originally Posted by Guffy
Nothing trumps a cute little saying
The cute little saying starts with the firing pin strikes the primer and then the whole thing, the case, powder, bullet and primer take off for the front of the chamber and stops when the shoulder of the case collides with the shoulder of the chamber, and then? The primer ignites. And that is it, nothing else.

I do not agree. My cases have artifacts that that prove that does not always happen then there is (pause, what's his name) HATCHER!!! Sorry about that. HATCHER SAID:

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Old August 23, 2015, 03:15 PM   #13
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Renegade19sc,

It's normal for cases to spring back a thousandth or so after being inflated by firing pressure to fill the chamber. That springback is why your RCBS PM is reading some of the cases short. Only if you are loading right up on the edge of getting sticky bolt lift, will a case mirror actual chamber size accurately. This is why you can get away with neck sizing cases only: until they have been fired a number of times, and assuming the load is not near maximum, that springback sees to it they still fit back into the chamber easily (though eventually they expand enough that it ceases to be so).

As far as headspace goes, keep in mind that the NO GO gauge is merely an upper limit for brand new chambers. It's not an upper limit for a rifle that has been fired. That would be the purpose of the FIELD REJECT gauge, which, for .308 is typically another 0.004" longer than the NO GO gauge. (IIRC, the SAAMI standard actually allows for 0.006" beyond NO GO, but the commercial gauges I have don't go that far.) So, if your rifle started out right at the NO GO length and had, as most commercial rifles do, at least slightly imperfect bolt/receiver lug contact, plus tool marks on both when new, then it might not take much shooting for that chamber length to to settle in another thousandth longer than when the factory measured it. On the other hand, if you had a new custom rifle with lugs that had been lapped to create even contact over a wide lug area before the chamber had been cut to fit it, depending how beefy the action was and how hot the loads were for the chambering, it could shoot thousands of rounds without appreciable change.

So, what does any of this matter? Unless you are trying to use the same batches of reloads in a number of different .308 rifles, not a whole lot. The fact is, as Mr. Guffey has described many times, you simply gauge your resizing to match the chamber. The most common way to do this is via a transfer measurement you take from cases fired in that same chamber. There are many ways to go about getting a comparative measurement for sizing a case to fit a particular chamber, but since you already own the RCBS PM, you should use that. It's a very good tool for this purpose. You are simply looking to adjust your full length sizing die to resize the case with its shoulder set back an additional thousandth or two from its as-fired size.

That procedure is, after all, what many wildcat cartridges have been. A chamber is made bigger than the parent cartridge's chamber (outside SAAMI standards for the parent). The cases are blown out by firing to fit that extra space, then subsequently resized to match that changed dimension. It works fine. Thus, even a chamber that goes over FIELD REJECT length can be treated as a very minor form of wildcat simply by sizing its cases for that chamber instead of for a SAAMI standard compliant chamber. All you lose is ammunition interchangeability with guns that have shorter .308 Winchester chambers.
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Old August 23, 2015, 05:29 PM   #14
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When checking a rifle's headspace, one should not force the bolt to close on a gauge. Any detectable resistance should be considered a non-closing.

I hand load. As long as I don't use commercial ammunition in my guns, headspace gauges have no use to me. I just size the brass to fit the chamber. It is safe to do so unless the dimensions are totally out of whack.

-TL
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Old August 23, 2015, 08:44 PM   #15
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OMG , I just happened to be looking in my notes and realized my numbers are the exact opposite of what I wrote . haha . I used to size my cases to 1.620 but now it's 1.618 oops . My notes say I used to be able to chamber a 1.621 but it was a little tight . Now 1.621 won't chamber in my rifle

ohwell never mind , forget what I've said . This goes to show . When reloading never go off memory always check your notes .
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Old August 24, 2015, 07:33 AM   #16
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Don'cha jus' luv it when a plan works out ?
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Old August 24, 2015, 07:44 AM   #17
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MG,

Like wool, you don't want to let your gun dry in direct sun after washing it in water.

Actually, if you've worked in the finish on the aluminum comparator inserts, shorter is exactly what you'd expect. This is one value to owning a good quality headspace gauge of known dimensions (be it GO, NO-GO, or FIELD REJECT). It gives you a constant calibration reference so you can monitor those insert results to see if they've changed, and as a bonus, if you are interested, you can get absolute readings by finding size relative to the gauge.
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Old August 24, 2015, 07:13 PM   #18
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Quote:
I have a rifle that will close on a No Go gauge. I have taken some fired brass from the rifle and measured it in a RCBS mic along with the no go gauge. Two out of three pieces of brass are almost equal to the no go gauge and the third one is a thousands greater.
What brand of rifle and what is your procedure for testing with the gage? Are you removing the firing pin mechanism and any bolt face mounted ejectors?
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Old August 25, 2015, 05:36 AM   #19
F. Guffey
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No clue what rifle we are talking about.
Quote:
What brand of rifle and what is your procedure for testing with the gage? Are you removing the firing pin mechanism and any bolt face mounted ejectors?
Quote:
This is one value to owning a good quality headspace gauge of known dimensions
I use head space gages, I use them as transfers and standards. I could have a chamber that allowed the bolt to close on a no go-gage, there is a good chance I would not know 'by how much'. That is the reason I make head space gages, I can save time by making one to fit all.

Then there is the push feed and the control feed. Always a problem when using a head space gage with a fixed length, again I like them. I have standards to check micrometers, nothing beats a standard when checking for zero.

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