So I'm an idiot.....CHS and exessive headspace

[sobrbiker883]

First I had a gasgun in 6.5 Creedmoor. For the gasgun I measured fired brass and comapred it to factory new brass and it was a couple thou more than new ammo from Hornady. "Cool", I think to myself and set up my FL die to size to the same size as the factory new stuff.

Fast forward a few months-

I have my local guy rebarrel my 7-08 boltgun with a Bartlien 6.5 for Creedmoor.

When he did my last tube, a 308, he gave me a few cases to set my dies from, at "0" and "+.001" and "-.002" for whether I wanted to make easy drop in rounds for comps, or over by a thou cases for tight seating for F-class, etc. So I'm confident he knows how to measure going into this barrel job....

After shooting a buttload of factory 6.5 Creedmoor in both rifles, I FL sized a bunch of brass. Some had been reloaded a few times too (3X fired).

The gasgun has since gone and I'm thinking "cool", I have over 400 pcs of once fired brass and a couple few hundred with a few firings for stock for my comp boltgun. Shittin' in tall cotton!

Shooting a match Saturday I had 7 out of 39 cases that fully seperated and quite a few that partially seperated.
WTF?!?!?!?!?

Notice I never mentioned measuring fired brass in my boltgun. I <span style="font-weight: bold">ASSUMED</span> that my guy (since he's a Creedmoor fan) chambered it close to factory since my 308 he did's "-0-" exactly matched FGMM.

Well, I measured fired brass from my boltgun to my sized stockpile and the fired brass measures 3.541/2" with a comparator, and my sized/new brass measures 3.532", no wonder brass with multiple firings shit the bed so soon!

Now I'm not sure if I should call him on it and have him cut the barrel for .009" or am I ok to just fire what I have (screening for an culling brass that has signs of imminent case head seperation), and then FL size to the chamber next go around????

Is .009" under a "dangerous" amount of excesive headspace for 1X fired brass or would that be pretty much just fireforming for the 400+ pieces I have? Would their life expectancy return to normal if I go back to properly bumping .002"?

The rifle shoots great with 1X brass and factory brass and I really hate down time with matches coming up...

I'm just pissed for not checking sooner, but it is what it is.

Thanks for the input in advance.

 

[notquiteright]

Re: So I'm an idiot.....CHS and exessive headspace

I had this problem in an older 7x57 mauser. I did not measure the chamber but new brass did not last past 3 reloads if full resized.

Now depending on your brass- thick walled is better and your load- hot loads flow brass quicker you can get longer brass life from just neck sizing.

Don't know the case dimensions of the Creed, but if it retains the body slope of the parent 308 case it will chamber under alot of dirty conditions. It will also brass flow, the rate depends on how tight the chamber and how hot the load.

I found remington brass, with it's thicker walls, to do better in fireforming than the much thinner walled winchester.

Now if it was me and I had a custom barrel chambered too long, I'd say something and see what can be worked out. I like a factory chamber but not one that wears brass out in 3 reloads.

Good Luck

 

[SONIC SAAMI]

Re: So I'm an idiot.....CHS and exessive headspace

I read your original post on this.

Someone attributed it to a bad batch of brass witch I knew was bullshit

As you found out case head separation is caused by excessive head space or bad reloading.

In your case you have traced it back to excessive head space..good job.



I take it you are using the Hornady D400 comparator is this correct?

Factory new 6.5 Creedmoor brass as measured with the D400 comparator comes in @ 1.530 from the datum line to the head of the case..

So long as you start with new or one time fired cases you should be fine with kicking them back to 3.540.

I'm sure someone on here will correct me if I'm wrong.



If it were me however matches or no matches I would take the rifle back and have it fixed.

I think you may find of you clean up the barrel shank and action threads and tighten and re-tighten the barrel a couple times the shoulders may crush up and correct your little problem. If that doesn't fix it have your smith take some off. Just be sure he still has the reamer incase he goes to far.

 

[bohem]

Re: So I'm an idiot.....CHS and exessive headspace

I would personally ask him to set the headspace to -0- as he did previously.

The factory spec for 6.5 gauges is GO and GO+.004 for no-go.

At 0.009" I'd be surprised if it wasn't out of spec actually and would close on a no-go.

For arguments' sake, the age old "GO, NO GO, Field" for 30-06 field grade blaster weapons is 0, .008, .011" (Somewhere in that area, my memory might be failing me here though, but you get the point.)

That's not match grade, that's just trench grade.

The way to fix it without having the guy fix it is to do this:

Neck up the brass to 7mm, then partially neck it down and leave a false shoulder on the brass. Load it and shoot.

The brass will headspace on the false shoulder created in the neck and then blow out to pickup that headspace issue.

This is common practice when dealing with AI's and things like the Dasher's and BRX's.

Again though, my suggestion would be to call him up, tell him what you found, and nicely ask that he remedies the issue.

Good luck.


<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I think you may find of you clean up the barrel shank and action threads and tighten and re-tighten the barrel a couple times the shoulders may crush up and correct your little problem. If that doesn't fix it have your smith take some off. Just be sure he still has the reamer incase he goes to far.</div></div>

If it was a couple tenths of a thousandths that might work, however it should not be necessary. If you're getting headspace change with tightening the barrel there is something yielding in the joint and that is BAD!

0.009" of headspace change is WAY BAD, even if you made it happen with tenon joint torque.

 

[aquinas]

Re: So I'm an idiot.....CHS and exessive headspace

The problem could be that he is using a hornady gauge.

Lemme splain:

Long ago, I purchased some headspace gauges for .308. The go- gauge measures 1.630 or minimum SAAMI spec. I popped the gauge in my hornady d400 and it read 1.627.

I ordered 4 more d400 bodies just to see what they would measure against my Forster Headspace gauge. They varied from 1.614 to 1.627.

The hornady gauge can only be used in a relative sense.

The way I do it now is to take a headspace gauge with a known measurement. Put that in a Hornady gauge and zero my calipers on the Forster gauge.

So let's say you use a 1.630 go-gauge and pop that in the hornady gauge and zero the calipers. Now read a piece of brass.

If it reads -.005...it's about 1.625 actual headspace. If it measures .003 it's about 1.633. Get it?

I think it's just a matter of time until someone gets blowed up becuase they used a Hornady gauge the way Hornady says to use it.

 

[sobrbiker883]

Re: So I'm an idiot.....CHS and exessive headspace

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: himaster</div><div class="ubbcode-body">The hornady gauge can only be used in a relative sense.
</div></div>
Don't care how they say to use it, I only see it as a relative too and wouldn't expect two off the shelf side by side to match.....close maybe, but not prefectly.


I am going to talk to the guy that cut it and se where to go from there. He's at Camp Perry, so I'll bug him next month.

I don't have any 7mm dies any more or I'd do the false shoulder on some. Hopefully my 6XC barreled action gets home from Bartlein soon and I can be distracted while I wait for my guy to get back.

Thanks for the input folks! Still can't believe I never measured any fored brass until 6 months after the rifle's been done and sizing hundred of pcs of brass for future use.....

 

[DavidAR10]

Re: So I'm an idiot.....CHS and exessive headspace

Have your chamber checked for gas cutting.

 

[aquinas]

Re: So I'm an idiot.....CHS and exessive headspace

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DavidAR10</div><div class="ubbcode-body">Have your chamber checked for gas cutting. </div></div>

What's that?

 

[DavidAR10]

Re: So I'm an idiot.....CHS and exessive headspace

When gasses escape through the crack in the brass. The brass has already formed to the chamber and the gasses can't escape easily between the brass and chamber walls. Some normally does and scares the hell out of the shooter that should be wearing eye protection.

The gasses say that they shall not be denied and start to "torch" into the chamber wall, called gas cutting.

If it happens to your match grade barrel from factory fodder...
even APA says that the ammo manufacturer owes you a barrel and a bolt.

It happened several months ago to a friend of mine and his FN. APA inspected and told him that the well known Georgia ammo manufacturer owed him a new barrel and bolt. Just so happened that ammo company called APA and asked for advice on how to proceed.

My friend received full payment of his FN rifle and put it toward the
DO IT ALL APR. He has brought in multiple 300yd targets that are sub-1.0" groups and 500yd targets that are sub-2.0" groups.

Hell, I guess gas cutting isn't so bad after all.