Case head Separation…in Sizing die

[gunsandgunsmithing]

The barrel has just over 700 rounds through it; the OEM barrel had over 2K rounds before replacement. And the cases - as stated - have not been tracked. That is my failure.

This is only the second case head separation I've seen so I can't say if that is typical or atypical. The thinning does appear very similar to the photos HERE . The text indicates the thinning is caused by repeated full length sizing that draws the case body longer with the resizing.

Gut feel on this is, it's due to my reloading/sizing process (full length every time).

Full length sizing every time, bumping shoulders back .002-.003 is standard operating procedure for most serious shooters, who load way hotter and yet get way more firings on their brass. If this is in fact what you are doing, why are your results different than everyone else's? I guess I just don't understand your gut feeling being what it is but it appears that you have made up your mind, at least in regard to not heeding my advice. I only suggest you look a little deeper rather than continuing to do the same and expecting different results. I think I'll bow out now and sincerely wish you the best of luck with finding the issue.

 

[AlNyhus]

Lots of unsupported case hangin' out the back of a too large chamber.....

 

[DaveTooley]

We agree the separation was in an unlikely place. So what could cause a thinning of the brass in that location. Here's a thought.

What if there was too much exposed case. Not to the point of being dangerous but enough to allow the case head to expand slightly over chamber base dimension's. This in an area where the FL die can reach it. The die hits the enlarged area and stretches' the case causing thinning. Same scenario/condition as bumping the shoulder back to far.

Yes I know the sizing forces are working to collapse the case right up to the point of reversing the press ram which would apply a stretching force.

 

[Alex Wheeler]

Looks like typical case head separation to me. For the brass to thin is has to migrate. When fired the brass grabs the chamber and the case head get pushed back to the boltface and the brass just in front of the head stretches and thins. The case gets longer because the brass is flowing forward. Unsupported case is different. It would swell and then get pushed back to where it was originally by the die. No thinning would happen. Work hardening could make it brittle, but if we are seeing thinning then its case stretch. Plus if it was unsupported enough to allow that much brass swell, I think this would have separated in the rifle by now. My guess is either the brass stretched a lot of the first firing or the shoulder is getting bumped more than we think. Its very common for the wrong comparator to give false numbers. Another mistake is to bump back based on a random fired case. You need to find your real zero. So you need a tight case then bump it to where the bolt barely drops then give it another .002 from that point. If you bump based off a case without finding the real zero you may be bumping .002 on a case that already had .002. The other thing to check is how much the case grows on the first firing. If its stretching alot on that first hit, its only a matter of time.

 

[sandwarrior]

I've had this happen, It was a sizing problem but I had way more sizing than you did. I wouldn't have expected this with the minimal resizing that you were doing.
Also, for whatever reason, your separation is way lower than mine and right where I would expect the case to be the thickest in the body.

FWIW, my separations came in a 7x57. at the top of the web (about 1/8" higher than yours). The main problem was that the chamber was cut .006" too deep. It worked fine while I neck sized. But, then when the cartridges started to get stiff going in I decided to full length size. That was a pretty large amount of brass to be moving, and the cases started failing.

So, how wide is the base of your die? maybe that is where the movement is happening too much? Or, I hate to say it, but Lapua may have had a bad batch of brass go out? Someone would have to cross section a new 6.5CM case to show what the web is to see, One other question is annealing. Clearly, you should nopt be annealing that low. But, if you aren't getting the brass soft enough up top, could it be putting extra pressure on the lower brass? I could see the CM's doing this as they are straighter walled than .308 based cases. Even Ackley improved cases

 

[jonbearman]

The paperclip should be bent 90 degrees at the end creating a stylus and sharpened so it will catch in the thin spot.

 

[DonB]

Yes. Trying to extract it but no success yet. I used One Shot case lube but either didn't use enough or....

This was a Redding FL body die.

I had this happen with a 7 mag. After trying several things I finally filled the case about halfway with epoxy and then drove it out from the top with a punch.