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Author Topic: advice needed: case head separation  (Read 470 times)

Offline CaNINE

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advice needed: case head separation
« on: September 10, 2017, 10:23:39 AM »
OK folks - last year I had a custom 300 Ultra built based off a rem 700 action. I recently had a case head separation. After doing some investigation I discovered that setting up my FL resizing die per the die instructions is oversizing my brass by approx. 0.008". After 6 or so cycles I'd finally created enough fatigue at the case head to cause a separation. So I've gotten a lot smarter and learned that I need to only set back my shoulder 1 to 2 thousandths and I now have bump gauges to make sure I'm within process.

During the investigation I checked my chamber with a set of PTG gauges. My bolt closes easily on the No-Go gauge. I can just start to feel some contact as the bolt cams over but no resistance.

I fired some new brass and it stretched approx 0.010 on the fireforming. You can see a slight line just above the case head where it stretched.

Of course I can minimize further fatigue by controlling shoulder set back but i'm wondering if brass life is already compromised because of this initial fireforming. RUM brass is not cheap.

I talked to the builder and he agreed that the separation was caused by me oversizing the brass and that all his chambers are checked multiple times to ensure they are within spec. I was advised to control my setback and all would be OK. I was fine with this approach until I saw the fatigue line after only one firing.

The builder is willing to check the chamber and if out of spec will correct the condition.

Is this something I should not worry about and just go on ensuring I control my sizing process better or should I have the builder correct the headspace? 

The first pic is the case head separation, second pic is new brass after one firing.

Offline Blacktail Sniper

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Re: advice needed: case head separation
« Reply #1 on: September 10, 2017, 10:33:03 AM »
Following...
It is better to be consistently incorrect than inconsistently correct...

Sarcasm: The ability to insult stupid people without them realizing it. 

My level of sarcasm depends on your level of stupidity...

Sarcasm makes smart people laugh and stupid people mad.

Offline Bill W

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Re: advice needed: case head separation
« Reply #2 on: September 10, 2017, 10:56:22 AM »
let us know if case life increases by adjusting your sizing die to minimize shoulder set back.  I would mike a fired case at the shiny juncture of web and case body.  That shine is showing just were the web ends.  Size a case the way you have your sizing die adjusted and then mike a case in the same area.  What's the difference as if you are overworking that area you will also have case life issues.

If you break a case off in your chamber use a threading die and take a turn or two in your case.  Use a cleaning rod to bump it out.  That's lots cheaper than buying a special tool to remove the case.  I've had it happen in the past to me and this is what I've used.  My other choice was to pay a gunsmith $25 to remove it and that was years ago.

Offline yorketransport

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Re: advice needed: case head separation
« Reply #3 on: September 10, 2017, 12:24:01 PM »
If your gun closes on a no-go gauge send the gun back to the smith. On a factory rifle I may adjust the die to make it usable but not on a gun I had built. I you pay a guy money to build a gun, he better fix it when it's not right. If possible, be there when he checks the headspace and bring your gauge with you. If he pulls the "all my guns are in spec" line again, ask him to verify that "specs" on the headspace gauge he's using are within industry specs and not just his own.

Any chance you'd give the name of the builder? The fact that he's willing to let you take the blame for an oversized chamber is pretty bad form. :twocents:

Offline Magnum_Willys

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Re: advice needed: case head separation
« Reply #4 on: September 10, 2017, 12:41:08 PM »
Try annealing your new brass first ?  You want to fireform the shoulder not the base, seems like your brass at the shoulder is not expanding as easily as it should.

When you say the brass stretched ? you mean overall length or you measured the shoulder and it stretched ?   .010 to the shoulder isn't that much for new brass, but is that what you measured ?

Offline hogslayer

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Re: advice needed: case head separation
« Reply #5 on: September 10, 2017, 02:11:49 PM »
Maybe I am slower than most in realizing that .002-.003 shoulder bump back isn't necessarily the same with a fired round as your chamber.  I lost lots of sleep over
Bumping my shoulders back .004 to .005.  But what I realized was to even get a fired case to rechamber took .002 bump back.  So 4-5 bump was actually 2-3 from the chamber. 

Offline CaNINE

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Re: advice needed: case head separation
« Reply #6 on: September 10, 2017, 04:42:45 PM »
Try annealing your new brass first ?  You want to fireform the shoulder not the base, seems like your brass at the shoulder is not expanding as easily as it should.

When you say the brass stretched ? you mean overall length or you measured the shoulder and it stretched ?   .010 to the shoulder isn't that much for new brass, but is that what you measured ?

I'm referring to the dimension from the head to a datum line on the shoulder using my bump gauge.  Virgin brass measures 2.462.  Fireformed brass measures 2.472. 
 

Offline Magnum_Willys

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Re: advice needed: case head separation
« Reply #7 on: September 10, 2017, 05:45:29 PM »
Try annealing your new brass first ?  You want to fireform the shoulder not the base, seems like your brass at the shoulder is not expanding as easily as it should.

When you say the brass stretched ? you mean overall length or you measured the shoulder and it stretched ?   .010 to the shoulder isn't that much for new brass, but is that what you measured ?



I'm referring to the dimension from the head to a datum line on the shoulder using my bump gauge.  Virgin brass measures 2.462.  Fireformed brass measures 2.472.

Dang I would of thought the soft shoulder would fireform .010 before the hardened base stretched much.  Interesting.

Offline b23

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Re: advice needed: case head separation
« Reply #8 on: September 10, 2017, 06:07:10 PM »
My problem with using the standard shoulder push back of 1 or 2 thou. on first firing brass is you aren't really sure it needs to be set back 1 or 2 thou. yet at all.  I go a step further and pull the firing pin and ejector plunger out of the bolt, chamber a piece of fired brass and see how easy the bolt handle closes.  With the bolt disassembled, if the bolt handle falls shut with no resistance, I don't push the shoulder back at all.  When I get a piece of brass that chambers and the bolt doesn't fall shut without resistance I measure that piece with bump gauge, push the shoulder back 1 thou. rechamber it and see how the bolt closes.  When I get a piece that won't quite close with just the weight of the bolt falling down, I measure that piece and set my sizing die so all my brass gets sized the same as that piece and I like having just a teenie little bit of a crush fit.

IMO, if you just set the shoulder back a generic 2 thou on first firing, you could still be sizing your brass more than it needs.


Offline CaNINE

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Re: advice needed: case head separation
« Reply #9 on: September 10, 2017, 06:42:16 PM »
My problem with using the standard shoulder push back of 1 or 2 thou. on first firing brass is you aren't really sure it needs to be set back 1 or 2 thou. yet at all.  I go a step further and pull the firing pin and ejector plunger out of the bolt, chamber a piece of fired brass and see how easy the bolt handle closes.  With the bolt disassembled, if the bolt handle falls shut with no resistance, I don't push the shoulder back at all.  When I get a piece of brass that chambers and the bolt doesn't fall shut without resistance I measure that piece with bump gauge, push the shoulder back 1 thou. rechamber it and see how the bolt closes.  When I get a piece that won't quite close with just the weight of the bolt falling down, I measure that piece and set my sizing die so all my brass gets sized the same as that piece and I like having just a teenie little bit of a crush fit.

IMO, if you just set the shoulder back a generic 2 thou on first firing, you could still be sizing your brass more than it needs.

B23 - what you described is close to how I now determine how much to set my shoulder back.  I've watched Broz' video over at Long Range Only.  I determine at what bump my chamber closes without resistance and then set the should back 2 thousandths beyond that point so I'm not really using a generic 2 thou.  I should have explained that it bit better in my OP. 

Offline Oh Mah

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Re: advice needed: case head separation
« Reply #10 on: September 10, 2017, 06:54:44 PM »
Just asking,Are you crimping if so how tight?I have only had separation issues when i over crimp.What are you using for O.A.L?How close are you to the lands? Let us know what the builder says about the chamber
"Boss of the woods"

Offline CaNINE

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Re: advice needed: case head separation
« Reply #11 on: September 10, 2017, 07:14:32 PM »
Just asking,Are you crimping if so how tight?I have only had separation issues when i over crimp.What are you using for O.A.L?How close are you to the lands? Let us know what the builder says about the chamber

I'm not using a crimp.  I am shooting Berger 230 OTM just touching the lands running around 2900 fps out of a 27" barrel.  The good news is that in spite of the headspace issue, the gun shoots amazingly well consistently giving 1/4 to 1/2 MOA performance with single digit ES.

Offline Oh Mah

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Re: advice needed: case head separation
« Reply #12 on: September 10, 2017, 07:32:23 PM »
very nice.did you have same problem with shorter o.a.l?
"Boss of the woods"

Offline b23

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Re: advice needed: case head separation
« Reply #13 on: September 10, 2017, 07:38:17 PM »
Everyone is different, but for me, to truly get a feel for things I fully disassemble the bolt. 

The tools required to pull the firing pin assembly and take the ejector plunger out aren't particularly expensive for a Rem 700 and I get an exact feel for what's really going on when I do that.  I've done it with the plunger still in but I much prefer to take it out because for me it gives me a more exact feel of what's going on and like I said earlier, I prefer to have a itty bitty bit of a crush fit and by fully disassembling the bolt I know exactly where that ever so tiny bit of resistance on the bolt is.

Offline CaNINE

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Re: advice needed: case head separation
« Reply #14 on: September 10, 2017, 07:43:38 PM »
very nice.did you have same problem with shorter o.a.l?

Yes.  The case head separation actually happened when I was seated about .050 off the lands.  But I don't think seating depth is playing a role here.  My understanding is it's a function of repeated expansion and resizing cycles with a chamber that is set up beyond spec, coupled with resizing the brass back 0.008 each time.

It sounds like I need to take the rifle back to the smith and have him verify that the chamber is set for proper headspace.

Offline yorketransport

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Re: advice needed: case head separation
« Reply #15 on: September 10, 2017, 08:34:49 PM »
This sounds like the perfect application for Plastigage!

Offline Oh Mah

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Re: advice needed: case head separation
« Reply #16 on: September 10, 2017, 08:40:38 PM »
very nice.did you have same problem with shorter o.a.l?

Yes.  The case head separation actually happened when I was seated about .050 off the lands.  But I don't think seating depth is playing a role here.  My understanding is it's a function of repeated expansion and resizing cycles with a chamber that is set up beyond spec, coupled with resizing the brass back 0.008 each time.

It sounds like I need to take the rifle back to the smith and have him verify that the chamber is set for proper headspace.
yes i agree with having it verified,Reason i ask is if it shoots as well as you describe seems to be a very well built rifle.A loose chamber most likely will not hold 1/2 moa.Have you tried farther out like factory around .150 from lands and see how well that magnum shoots and if it still causes the separation?
"Boss of the woods"

 

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