Anatomy of my Case-Head Separation...

[oneshot onekill]

The pictures below show the progression of the Case Head Separation I recently experienced with FGMM Brass after only 2 reloadings. In each picture the shell on the left is from after the first firing of New FGMM 168gr bullets. The middle shell is after neck-sizing and firing 155gr SMK's with 43gr of Benchmark and CCI200 Primers behind them. The shell on the right is the second reloading and those were full length sized 168gr SMK's with 43gr of IMR4064 and CCI200 primers behind them. After neck-sizing I only checked the case length but none of them needed to be trimmed (as expected).

My Dremel-fu is lacking so the cuts are a little sloppy but you can pretty clearly see the first shell looks OK and is pretty clean, the second is showing signs of thinning walls and is a little more dirty. The third has failed...

 

[karagias]

Re: Anatomy of my Case-Head Separation...

In which rifle did this take place?

 

[oneshot onekill]

Re: Anatomy of my Case-Head Separation...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TheodoreKaragias</div><div class="ubbcode-body">In which rifle did this take place? </div></div>
The rifle is an HS Precision RDR. The Headspace on the rifle is not excessive. I'm still working on figuring out what went wrong. It was just a fluke that I had empty brass from each firing.

 

[buffybuster]

Re: Anatomy of my Case-Head Separation...

Do you have a longer than SAMMI spec chamber or are you setting back the shoulder too much? Two reloadings seem too few, even for Federal brass.

 

[oneshot onekill]

Re: Anatomy of my Case-Head Separation...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: buffybuster</div><div class="ubbcode-body">Do you have a longer than SAMMI spec chamber or are you setting back the shoulder too much? Two reloadings seem too few, even for Federal brass. </div></div>
To my knowledge the chamber is a standard .308 chamber. I checked the brass with an L.E. Wilson Case-Length Gauge but I now understand those are not very accurate.

 

[karagias]

Re: Anatomy of my Case-Head Separation...

You need to use head space gages. Typically there is a go and a no-go. Bolt should close on go and should not close on no-go. A local gunsmith will likely have gages or you can buy them from Pacific Tool and Gage.

 

[vman]

Re: Anatomy of my Case-Head Separation...

yeh go and no-go guages are typically something a smith will use on a freshly cut chamber.

Go should allow the bolt to close, no-go should not allow the bolt to close. If a no-go guage chambers fully, your rifle has problems ie, excessive headspace.

oneshot, is that primer on the third firing looking a little flat to you?

Im not sure on Benchmark powder, so I cant comment on 43.0 grains.

Double check a few things.

1) are you have execise pressure signs showing
2) get a hornady guage set and check if your brass is being sized properly, which relates back to how you set up your sizing die
3) if you believe the above is fine, run a no-go guage thru the chamber and see what happens

 

[oneshot onekill]

Re: Anatomy of my Case-Head Separation...

I checked the chamber with a no-go (actually a "field" gauge) and the bolt was nowhere near closing so that's not it... Thankfully! There is the possibility I over-sized the brass when I full-length sized it but the middle picture shows signs of starting to thin and it was the first reloading of "fired once" brass and was neck-sized ONLY. All of the cases that split show signs of over-pressure but I assume that is a side-effect of the case-head separation because the second reloading was done to SAAMI specs and only had 43gr of IMR4064 in them.

 

[token5gtd]

Re: Anatomy of my Case-Head Separation...

this is strange, i've got 40 Federal cases i've loaded 7 times so far, annealed once... and they look like i may get 2 or 3 more out of them.

granted these cases have been assigned to reduced loads (28.5 4198 - 180gr Sie PH) i've been pretty happy with their performance.

 

[oneshot onekill]

Re: Anatomy of my Case-Head Separation...

Interesting thing I just noticed looking at the pictures. Even the one on the far left which was a brand-new bullet looks to be a little dis-colored in the area of the separation.

 

[former naval person]

Re: Anatomy of my Case-Head Separation...

It is headspace...not the rifle, but created by the sizing of the case. Do a few more firings on a neck sized case (same one each time) and see if you are having a continuing problem. You'll get a little stretching on the first few firings, but if you don't set the shoulder back excessively it should not continue. I think what you are seeing on the second case in the picture shouldn't worsen with proper neck/FL sizing. JMHO

 

[Grump]

Re: Anatomy of my Case-Head Separation...

I'm with FNP above.

My first batch of FC .308 brass had only *some* fail on the second reload, but that was with FL resizing every time. And too much at that. I've even identified a rough idea of how much shoulder setback can vary depending on whether the case lube was a bit "light".

Some are about like your middle pic brass. When I'm bumping the shoulder back by .005 or less, they are lasting at least two more reloadings. Don't know how many more because I'm only on reload #4 so far.

BTW, this frequency of failure with "full" resizing, camming over the ram hard into the bottom of the die (THREE different makes, by the way) is pretty much identical with USGI brass too.

For perspective, the traditional"full" resizing takes the cases down to the minimum on the Wilson case gage. Fired cases from two different chambers extend a bit *above* the max cartridge dimension on the Wilson gage. I'm now sizing so the cases are still a tiny bit "long" per the Wilson gage, but the rifle is happy with the ammo and the cases done that way from first resizing show not a trace of thinning at all after three reloads.

Yup, this is also all in a semiauto. but my son's Lapua brass fired from a Remington 700 SPS Varmint lasted through 7 firings with the over-sizing. I think that chamber was much closer to Wilson case max on fired cases.

I'd give you numbers, but the .001 calipers seem to have vanished.

 

[Fred_C_Dobbs]

Re: Anatomy of my Case-Head Separation...

Great pixs, oneshot. I done archived them.