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'Flattened' primer pictures?

 
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  #1  
Old 11-04-2006, 06:20 AM
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\'Flattened\' primer pictures?

A long time ago,30yrs or more, I basically taught myself to reload. I was using a fairly hot load in a 25-06. I did not realize that it was hot, until a helpful reloader showed me that all of my primers were flattened. I know what they look like, but would appreciate someone posting pictures. I'd like to show some newbie buddies. Thanks, capt david [img]/ubbthreads/images/graemlins/grin.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img]
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Old 11-04-2006, 07:16 AM
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Re: \'Flattened\' primer pictures?

Flattened primers are not always a sign of pressure - more often, they are a sign of head space.

To read pressure, you need to take into account many signs all at once.

Cratering of the primer: Assuming that normal factory loads DON'T crater, then cratering is a sign that you are pushing it. These days, with the loose tolerances of manufacturers, some bolt pin holes are way oversized and will crater with light or factory loads.

Flat primers: Assuming a normal rifle with a proper sized pin hole... cases will crater before the outside edges start to smear out to the case and get a sharp edge. So with cratering and flat primers it is clearly a case of excess pressure.

BUT... in most situations, there is some space between the bolt face, and the brass. Even a rifle that is "in spec" can have as much as 0.025" of headspace... in fact it is extreamly rare that a rifle has "0.000" headspace.

With this space, when the cartridge is fired, the primer pushes the case forwards 'til it hits the shoulder, during which time the powder lights. At this stage, the primer is sticking out of the case by the amount of headspace - (ei 0.025"). The pressure in the case then forces the case back against the bolt face.

NOW... if the primer walls are firm against the pocket walls, then the protruding primer gets squshed and flattens out - but there is no excess pressure.

So, in order to use flatened primers as a pressure sign, they must also be read with other signs.... mostly cratering.

Reading primers is an art, not a science.


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Old 11-04-2006, 07:27 AM
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Re: \'Flattened\' primer pictures?

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Old 11-04-2006, 07:28 AM
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Re: \'Flattened\' primer pictures?

Different brands of primers are made out of different metal. After a while of shooting the same brand of primer you can get a feel for the primer. Federal 215's are relatively soft and I don't worry until there is a crater and all of the round bevel of the edge is gone(Samspade's primer #3). That is also based upon guns with Wby freebore which is a good safety feature for people who push guns to the limit. Additionaly, I will compare primers between different powder loads from the same chamber to help.

The repriming operation is also a good time to evelaute your load. If the primer pocket is loosened then you are appraching the limits of that brand of brass.
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Old 11-04-2006, 07:22 PM
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Re: \'Flattened\' primer pictures?

[ QUOTE ]
Even a rifle that is "in spec" can have as much as 0.025" of headspace... in fact it is extreamly rare that a rifle has "0.000" headspace.

[/ QUOTE ]What rimless bottleneck cartridge has a NO-GO headspace .025-inch greater than GO headspace that's within SAAMI specs?

A lot of "partially full-length sized" cases (full length sizing die set to size less than all of the neck) have zero headspace in the rifle they're used in. And a large number of neck only sized cases have about .001-inch headspace and some will get down to almost zero in the rifles they're used in.

Are you sure of your numbers?
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Old 11-04-2006, 09:01 PM
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Re: \'Flattened\' primer pictures?

There are two kinds of "Head space"... the first is the minimum to maximum chamber dimensions, what is most often referred to when speaking of "HEAD SPACE" (in capitals) - which for, say the .223 is:

(ANSI/SAAMI Z229.4-1992)

To the 0.330" datum line, 1.4736" max and 1.4636" min. so the rifle chamber has 0.010" between minimum and maximum chambers from the factory.

Add another 0.005" for a field gauge and a rifle can be with in spec with a spread of 15 thou.

But to arrive at the real "working head space (little letters) add to this the case variations:

Cartridges have their own set of min/max dimensions...

... and here the .223 case (to the 0.330" datum line) would be 1.4666" max and 1.4596 min.

So the best combination would always be the minimum chamber and maximum case, which would be:
Chamber = 1.4636"
Case = 1.4666"
Which would be a case that was 0.003 over sized, giving you a crush fit.

But the opposite is also possible. A maximum chamber with a minimum case.

Chamber = 1.4736"
Case = 1.4596"

Or 14thou of working head space...

But there is a third variable.

I'm sure that you are aware that SAAMI specification are not mandated measurements. The set of books from SAAMI state "Voluntary Industry Performance Standards", which is a polite way of saying, "Please guys, try to stay inside these limits".

Most good custom gun builders do stay inside these limits, but in large factories (especially in the US), the adherence to these recommendations are loose and will easily add another 5 thou under production pressures.

To that, add the wear of the locking surfaces as the tool marks are rubbed off in the first weeks of shooting, and you have an easily achievable worst case of 25 thou of working head space.
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Old 11-05-2006, 06:17 AM
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Re: \'Flattened\' primer pictures?

Catshooter, .025" of excess headspace is going to give far greater problems than flat primers. I strongly urge anyone that has a rifle, with more than .004" of headspace, to avoid shooting it.
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