Can these marks on my cases be something other then ???

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M

Metal god

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Tool marks from my chamber ?

fI1d62.jpg


These cases were fired in a new AR-10 type upper I bought recently . I originally thought they were tooling marks imprinted on the cases when fired . I how ever now have another thought .

When I first received the upper I ran a bore snake through the barrel then tested a the headspace with a GO and NOGO gauge . It passed both or so I thought . I did not strip the bolt and how I tested it was to ride the charging handle home then use the forward assist to force the bolt closed . It worked on the GO gauge and appeared to work on the NOGO gauge .

On the NOGO I felt and heard the bolt snap over the extractor while pushing several times on the forward assist but the bolt did not go into full battery . I at the time wrongly assumed this meant the bolt passed the NOGO gauge as well . Fast forward to a few days ago and me measuring the head to datum measurement on the cases I fired and they all are coming out .004+ longer then my Forster NOGO gauge measures . :confused:

So I tried the NOGO gauge again with out stripping the bolt but this time I had the upper off the lower and used a light rubber mallet to hit the base of the BCG to force the bolt closed . I gave it a couple firm hits ( not hard by any stretch ) and sure enough the bolt went into full battery on the NOGO gauge . :( Unfortunately I don't own a field gauge in this cartridge but I don't think it matters because it should not fail the NOGO gauge so it's going back regardless .

OK now all that said . I'm already getting casehead stretch at the web on factory new ammo fired in this upper that are already failing the paper clip test :rolleyes: So not only is the headspace long , it may be dangerously long which brings me to my over all question .

Can those marks on the cases be stretch marks along the length of the case ? Meaning the case is stretching in multiple locations along the case body and not just the web do to the excessive headspace problem I appear to be having ?

Or what about scratch marks created as the case slides back to the bolt face under reduced pressure just before extraction or even upon extraction when still under some pressure ??

FWIW I have a email into the manufacture asking for return and repair/replace . I'm assuming since the 308 AR platform does not have a shared industry standard barrel extension and bolt dimensions . Rather then replacing the barrel they will likely just find a bolt that gives the correct headspace ???

Anyways what do you think ?

MG
 
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While I would like to see cleaner looking spent cartridges it does look like the chamber could have a cleaner nicer finish. I doubt they are stretch marks.

I would be more concerned with the numbers as to how much the cases grew when fired.

On the NOGO I felt and heard the bolt snap over the extractor while pushing several times on the forward assist but the bolt did not go into full battery . I at the time wrongly assumed this meant the bolt passed the NOGO gauge as well . Fast forward to a few days ago and me measuring the head to datum measurement on the cases I fired and they all are coming out .004+ longer then my Forster NOGO gauge measures .
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A 308 Winchester Go gauge should be 1.630" with the No Go at 1.634" and a chamber cut to SAAMI specifications, especially on a new rifle, should not allow the bolt to close or in this case rotate into battery.

If the scratch marks were perpendicular to the case head I would maybe think about the case being dragged out during extraction but they aren't.

I'm already getting casehead stretch at the web on factory new ammo fired in this upper that are already failing the paper clip test So not only is the headspace long , it may be dangerously long which brings me to my over all question .
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What do I think? I would be doing as you are doing and looking to have the manufacturer make the rifle right.

<EDIT>
I just thought about something you may want to try. If you have any shim stock with stainless preferred I have used a single hole punch to punch out pieces of shim stock and using a small dab of any grease stuck my punch outs to the head of my headspace gauges. Just as an example 0.002" shim on a No Go gets you out to 1.636". Double that with two pieces and you have a 1.638 Field gauge.
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Ron
 
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It doesn't seem to be stretch marks. All the case separation I have seen had single ring before it broke. It is the weakest point in the brass and that would be where it eventually broke.

When checking headspace with gauge, one shouldn't try hard to force the bolt to close. For "go" gauge, the bolt should close without any felt resistance; it fails otherwise. For "no-go", any felt resistance before full battery is a pass; fail otherwise.

-TL

Sent from my SM-G930T using Tapatalk
 
Other questions might be what were the loads you were using, what is the barrel stamped caliber and is the brass new or resized?
 
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First of all, the headspacing on most 7.62 NATO chambers will run 0.006 to 0.010 inch longer than their sporting rifle counterparts, to allow for proper feeding and ejection during repeated, rapid firing. Combine a longer chamber with a thinner case—the .308 Winchester cases will be thinner than military 7.62 NATO cases- and you open the door for the possibility of a ruptured case.
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https://www.shootingillustrated.com/articles/2018/8/19/308-win-vs-762-nato-whats-the-difference/

I see 2 things i dont like. 1. Not cleaned properly, (bore snake). 2. Misused head space gauges.
 
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Reloadron , I have some feeler gauges but no way to cut them clean enough to where the edges won’t be flared up which would scew the measurements.

Tangolima , I did not strip the bolt and the way AR’s bolts close when the rifle is assembled there is some force needed . When I’m assembling from parts I’ll strip the bolt and check the headspace before installing the barrel . I’ll often cast the chamber as well .

FWIW the gauge ejected as if it was a normal round being ejected . No resistance or extra force needed on the charging handle .

Zeke , I always use factory new ammo to test any new firearm . In this case I used Winchester 150gr soft points and Federal 150gr flat nose/point . Both appear to be there standard hunting loads . Barrel is stamped 308 Winchester.

243winxb , On your first point I was not so much cleaning the new barrel as I was clearing out anything that may be in there from after manufacturing and shipping as I do with all new firearms . On your second point although I do agree I did not test in the optimal way and addressed why in earlier posts . Regardless of how I did it the bolt should not have closed on the NOGO gauge . It not like there was a large cam force exerted allowing the bolt to close and the fact it ejected easily indicates the bolt was not binding on the lugs/barrel extension .
 
When I came to think about it, the headspace does seem on the excessive side, or the bolt won't close you force it or not. Even if it passes the no-go with felt resistance, it would be passing marginally.

As a brand new rifle, the rough chamber along is enough reason for returning to the manufacturer.

-TL

Sent from my SM-G930T using Tapatalk
 
Metal_god, when I mentioned:
I just thought about something you may want to try. If you have any shim stock with stainless preferred I have used a single hole punch to punch out pieces of shim stock and using a small dab of any grease stuck my punch outs to the head of my headspace gauges. Just as an example 0.002" shim on a No Go gets you out to 1.636". Double that with two pieces and you have a 1.638 Field gauge.
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What I had in mind was just plain flat shim stock along these lines. I only suggested stainless steel because of the durability. You only need a few sheets not a bundle. Then a simple single hole punch. That punch will do fine for light stainless shim stock. I don't suggest hacking up some good feeler gauges.

Doing this with a tiny dab of grease allows you to extend a Go, NoGO or even field gauge in 308 Winchester to get a good idea of where you are at. Any hardware store should have both.

Ron
 
Ron , haha that was not the type of hole punch I was thinking of . I'm sure I have one of those around here somewhere . I've already cut on my feeler gauges so that set should work just fine .

Thanks MG
 
So I tried the NOGO gauge again with out stripping the bolt but this time I had the upper off the lower and used a light rubber mallet to hit the base of the BCG to force the bolt closed . I gave it a couple firm hits ( not hard by any stretch ) and sure enough the bolt went into full battery on the NOGO gauge . Unfortunately I don't own a field gauge in this cartridge but I don't think it matters because it should not fail the NOGO gauge so it's going back regardless .
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I have said the field reject length gage is not necessary I have also said a smith with a field reject length gage can do without a go-gage and a no go-gage.

F. Guffey
 
Rough chamber. ...Seemingly, with a headspace issue.
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Frank, again: I have a rifle that has a field reject length chamber +.002". That means I have .016" clearance between the shoulder of a minimum length/full length sized case and the shoulder of my chamber.

Because I am a reloader and my dies and presses have threads I do not have an excuse for shooting short* cases in my long chambers.

F. Guffey

*Short chambers: Short from the datum to the bolt face.

And then there are short chambers. When sizing cases for short chambers I run out of threads on my presses. Not a problem for me because there are creative ways/methods/techniques available to me when sizing cases for short chambers.
 
As a brand new rifle, the rough chamber along is enough reason for returning to the manufacturer.
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I know shooters that like ridges in the chamber , they believe the swirls hold the case more better;). I don't, when I look at the chamber I want to see a mirror finish. I believe 100% contact between the chamber and case is as good as it gets,

Some like 'the cross hatch' for break-in.

F. Guffey
 
I doubt they are stretch marks.
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You should know those marks are not caused by stretching, understand I am used to dealing with reloaders that are in the habit of making this stuff up.

F. Guffey
 
Agree, rough chamber. A stretch ring would be showing up about where the reamer marks STOP near the head.

Snapping the extractor over the headspace gauge is not proper operation.
A stripped bolt and fingertip pressure for accurate readings.
 
Look at the FlexHone rifle chamber tools for removing those marks. Takes about 30 seconds each with a coarse and fine one. That won't fix the headspace though. A new chamber should be between the minimum and +0.004" over that. Allowing about -0.001" spring-back after fireforming, then your chamber sounds like it is about +0.009" over the minimum, which exceeds a commercial Field Reject gauge, which is usually +0.008".
 
Look at the FlexHone rifle chamber tools for removing those marks. Takes about 30 seconds each with a coarse and fine one. That won't fix the headspace though. A new chamber should be between the minimum and +0.004" over that. Allowing about -0.001" spring-back after fireforming, then your chamber sounds like it is about +0.009" over the minimum, which exceeds a commercial Field Reject gauge, which is usually +0.008".
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If it was a 30/06 chamber the field reject length gages would be .014" longer than a minimum length full length case unless the case has head space; all that is required when the case has head space is up to the reloader. All he has to do is make it up.

And then there is the problem with nailing all these numbers down, reloaders have tolerances, +luses and -minuses, variations etc..

To fix the head space: I do not know what reloaders do with their cases because some of them have case head space. I do not have case head space, I off set the length of the chamber with the length of the case. The length of my chamber is measured from the datum/shoulder to the bolt face and the length of the case is measured from the shoulder/datum to the case head. The difference in length between the two is clearance.

So if the OP has too much clearance he needs to lengthen the case from the shoulder to the case head, again, this will off set the length of the chamber.

Again: I have a M1917 that has a chamber that is .014" + .002" longer than a minimum length full length sized cases. That means the chamber is .011" longer than a no go-gage length chamber. For me is a small matter of adding .014" to the length of the case between the shoulder and case head. And again; that gives me the magic .002" clearance.

And then there is all of this hoopla about "Where is the case head". When I want to know where the cases head was and or is when the trigger is pulled I measure the case, for me that is easy because I do not have cases with head space.

F. Guffey
 
If you look at the OP he says:

Metal god said:
I'm already getting case head stretch at the web on factory new ammo fired in this upper that are already failing the paper clip test So not only is the headspace long , it may be dangerously long…
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That surprises me, and it is exaggerated by hard case grip on the rough chamber, but it sounds like the result is these cases stretching a lot more than the chamber headspace numbers suggest it should be. Otherwise, I would just suggest he resize to match the chamber less about 2-3 thousandths for the AR10. The only thing I can suggest to try is Slamfire's method of lubricating cases to spread the stretch out over more of the wall on the first shot. I would apply the Flexhones to the chamber to get rid of the toolmarks first, though.
 
I first used the flex hones in a military chamber that was very rough. It left the fired cases with a sandblasted appearance. The flex hone quickly cleared the problem and now no more messed up brass.

They are not available in all chamberings but the most common. I don't know if custom hones are available, but it might be worth asking them about it.
 
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