Did someone mess with your sizing die? Maybe it was resized too far? Are you full sizing or neck sizing spent cases from YOUR rifle only?

Is the primer pockets loose in the cases with blown primers?

The primers fall out completely and have much play in the primer pockets. The web and rim of the case is so enlarged that it does not fit the shoe of the reloading press.

I have regularly found a small ring on the primers from this batch of cases. It looks like a little wall around the dent made by the firing pin. Every time I checked speed, everything was on spec so I never bothered with that.

Did you measure the velocity of the shots where the primers were blown?

No. I calculated the average volume of a batch of almost 200  PMP cases, then used QL to calculate a safe load for practice. Then I loaded a batch of cartridges with the safe load.

Who loaded the ammunition?

I did; I started reloading 33 years ago.

Were the cases annealed by you or someone else?

No. Most if then were once fired when I received them. They have not been fired more than five times. Thrice is probably correct.

Have you had any head-case seperations?

No. The two cases I have show lines which might indicate it.

What is the case growth per shot?

I have never measured that in my life.

A carbon ring will give pressure every shot so we can discount that theory.

The rifle stays accurate, but these "blown" cases usually throw the bullet towards the low right side on the target.

Did someone mess with your sizing die? Maybe it was resized too far? Are you full sizing or neck sizing spent cases from YOUR rifle only?

The chances for someone messing with my dies is fairly small, simply because I am the only one handling it.

I tried neck sizing for a while and went back to full length sizing after I couldn't load a cartridge on a hunt.

No. Most if then were once fired when I received them. They have not been fired more than five times. Thrice is probably correct.
quote.
You speak of these cases as received 1 x shot, are the second hand cases? If so can we then agree that these cases could then be almost any number of times shot.

No. Most if then were once fired when I received them. They have not been fired more than five times. Thrice is probably correct. 

You speak of these cases as received 1 x shot, are they second hand cases? If so, can we then agree that these cases could then be almost any number of times shot?

I know/knew the original owners of the cases. They bought factory ammo and did not reload. Thus I received (most probably) once fired PMP brass from them. I did not count the amount of times I reloaded them. Given the amount of shots fired, I did not reload them more than three times.

"The primers were indented at times, and sometimes pushed flat, and blew out three or four times."

"The webs of the blown cases were far out of specs."

"The primers fall out completely and have much play in the primer pockets. The web and rim of the case is so enlarged that it does not fit the shoe of the reloading press."

"I have regularly found a small ring on the primers from this batch of cases. It looks like a little wall around the dent made by the firing pin."

The above are all signs of high pressure loads. Enlarged webs can theoretically be caused by excessive headspace. Cratering can also be caused by an overlarge firing pin hole in the bolt.

Enlarged primer pockets can only happen with more pressure than the brass can handle. Couple that with the expanded web, sticky bolt lift, primer cratering and blown primers, then overpressure or soft brass are the only explantions.

So, you may have excessive headspace. That can easily be solved by setting up your sizing die correctly. I do not believe your blown primers are as a result of excessive headspace. I believe that you also have a problem elsewhere with regards to loading.

How do you measure the charge weight; powder measure or scale?
Where did you get the bullets from? Are they all the same brand, model and weight?

The only other way that you can get excessively expanded webs and primer pockets is if the web itself was annealed. Which is difficult as you used these cases before and you didn't anneal the brass..

In your shoes I'd scrap the whole batch and start from new. I'd also check each bullet from this batch for weight and shape. And weigh every charge.

Good Morning ,

Was there any resolution to this problem ?

What was the outcome ?

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While we wait for that future answer ...

Personally I think something wrong with the  chamber far worse than just normal headspace

"The web and rim of the case is so enlarged that it does not fit the shoe of the reloading press"

I find it hard to think that the rim can be enlarged ?

There is a small portion of the web that is not supported when the round is chambered

Get out the measuring tools and measure everything - I would also do a chamber cast

Even better still get the rifle to a really good gunsmith and let him do all the checking.

Hi, another thing to check is if the chamber is dirty and needs to be cleaned/ polished. I had it recently on the 308 while on course. Probably a bit of dirt got in on a previous range session and the the on course the bolt stuck on the first shot with factory ammo. No signs of pressure on the case. Second shot the same. Had to give it a good cleaning before it was shooting normally. Took it to the gunsmith to polish and make sure all as ok. Cases had scratch marks from the dirt. Been shooting normally since then. I make sure to check if a case has fallen down to clean it before inserting into the mag so no dirt gets in.

Posted by: @newton

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Good Morning ,

Was there any resolution to this problem ?

What was the outcome ?

================

While we wait for that future answer ...

Personally I think something wrong with the  chamber far worse than just normal headspace

"The web and rim of the case is so enlarged that it does not fit the shoe of the reloading press"

I find it hard to think that the rim can be enlarged ?

There is a small portion of the web that is not supported when the round is chambered

Get out the measuring tools and measure everything - I would also do a chamber cast

Even better still get the rifle to a really good gunsmith and let him do all the checking.

**************************************
Why would chamber change from shooting to problems, what could change ?

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I have had three or four blown out primers in my 308 over the last year or two.

By my experience, the loads are over  pressure. The loads are borderline too hot, and the odd one is showing it by spitting the used primer. It'll occur more frequently as you re-use that brass, because the primer pockets will have stretched after a couple of firings, and it'll get to the point where you can seat a new primer with your fingertip. If you are looking at the shape of the fired primer, or a sticky bolt or extractor marks, and nothing there is telling you it's over pressure, then you are experiencing the reason why I always say nobody's eyes can measure chamber pressure, unless they are looking at the measurement on a 1/10,000 micrometer.

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Yesterday we determined that the headspacing was too much. The bolt closed stiffly with six patches of masking tape on the back of the case.  

Two things I've experienced that can cause this :

1. commonly - a lack of attention to the setup of the sizing die

2.  uncommonly - the barrel is not torqued enough and unscrewed itself half a thread. This shows up on an incorrectly torqued barrel when you try to remove a silencer or brake that's been on the rifle for a while. or try to remove it when the barrel is hot.

Headspace issues still do not stretch primer pockets, cause heavy bolt lift, enlarge case heads and cratered primers.

Thanks for all the input

STILL waiting for OP to tell us what he discovered  - as the cause ????

When one reads from the beginning one can read that the OP is quite sure that he is NOT loading anywhere near .. pressure levels

Loading for 33 years