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Flattened primers?

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Old 10-31-2013, 10:10 PM
Bronze Member
Join Date: Nov 2012
Posts: 40
Flattened primers?

I have attached a picture of two brass recently fired from my 7mm Dakota. The one on the left with extremely flattened primer was a new piece of brass loaded the exact same as the brass on the right which had been fired for the third time and only neck sized. The only difference between the two loads was the new brass head space was 2.062 and the neck sized brass was 2.079. Should I have two back the charge off on forming new brass as the excess head space could cause excessive pressures???
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Flattened primers?-img_20131031_204132_488.jpg  
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Old 11-01-2013, 05:43 AM
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Join Date: Dec 2005
Location: Tucson Az
Posts: 1,282
Re: Flattened primers?

I believe the cartridge was able to move forward with the firing pin strike. When the pressure began to build the primer had enough space to be pushed partway out of the primer pocket. As the pressure continued to build the brass moved rearward mashing the primer into the bolt face. The excessive headspace caused this issue not excessive pressure. If you pop out a fired primer you will see a mushroom shaped head on the primer.

I hate to say this but you are going to have to make a false shoulder on the neck or seat a bullet out so it touches the lands and fireform these short cases. It is hard on the brass to stretch in the manner where it has room to move and could cause damage is where the web meets the case body.

Somehow your rifle was machined with excessive headspace or the virgin brass was made too short.
If this is a recent build you might consider talking to the builder and have the headspace reduced.
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Old 11-01-2013, 06:09 AM
Silver Member
Join Date: Nov 2009
Posts: 298
Re: Flattened primers?

Your measurements indicate you have a generous chamber in your gun.

Neck sizing will get you a better fit and you might even see better accuracy with neck sized loads.

At some point you will have to bump the shoulder back. Adjust your FL die to give you minimum shoulder set-back (~.002") to extend the life of the brass.

I don't think you have to reduce your load.

I had a similar situation with my Ruger #1V 25-06, generous chamber. I ended up buying a body die to better control shoulder bump.
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Old 11-01-2013, 06:33 AM
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Join Date: Nov 2012
Posts: 40
Re: Flattened primers?

So the only thing to worry about immediately will be shortened brass life, no other concerns? How do you make a false shoulder. I try to neck size mostly but after a few firings I start to get a stiff bolt lift and end up FL sizing to set shoulder back. Thanks for the replies.
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Old 11-01-2013, 06:49 AM
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Join Date: Dec 2011
Location: Michigan
Posts: 1,082
Re: Flattened primers?

Originally Posted by snojnke View Post
So the only thing to worry about immediately will be shortened brass life, no other concerns?
Just my opinion, but I would not be comfortable firing brass with 17thou excess headspace. Even the possibility of a major issue (a-la case head separation) is enough to make me re-evaluate. That 17 thou has to come from somewhere.

While I agree you can most likely fireform using a false shoulder, this is a band-aid only - you still have a long chamber or short brass. I don't like "special case" guns. When only the operator knows how to run it safely, the possibility exists of issues in the future as it gets passed down, sold, etc.....

I would try to get some measurements from other virgin brass to see which of the above it is. If it is a brass issue, I'd see if the manufacturer would replace it. If a chamber issue, I'd have it fixed.

My 2C only.
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Old 11-01-2013, 09:29 AM
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Join Date: Apr 2007
Location: Fort Morgan, Colorado
Posts: 327
Re: Flattened primers?

snojnke I had a custom put together some years ago that had a generous chamber similar to the rifle you describe, and I neck sized the brass and when the bolt lift became stiff I would use a FL sizer and set the shoulder back just enough to make them work. I then had to use the neck sizing die to finish them. I don't think this is detrimental to the life of the brass as long as it isn't over worked, such as complete FL sizing would.
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Old 11-01-2013, 09:51 AM
Bronze Member
Join Date: Nov 2012
Posts: 40
Re: Flattened primers?

The only supplier of 7mm Dakota brass is Dakota themselves, I'm not sure who is manufacturing it for them. At one time it was Norma not sure now though. I have ordered several batches and the have all been consistent at 2.062. I obviously have a generous chamber just don't want anything bad to happen.;
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