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Pressure Signs

 
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  #1  
Old 11-27-2013, 12:10 PM
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Pressure Signs

I came across this issue last weekend while shooting a 7 - 08. Things I look for in load development are as follows:

Primer flattening and cratering
Sticky bolt lift on up cycle and recycle
Extractor hole mark/ring

Some times I have seen primer issues without the rest of the signs and don't get all worked up over it. Well, unless the primer is just hammered by pressure. I tend to get much more concerned when I see extractor marks and bolt lift issues.

So, the issue came when I shot some PPU ammo. A little cratering, no bolt lift issue, but I did see and extractor ring mark. At max grains of 4064 I did not see signs on this PPU brass. I think I can go up 1 grain more but have not tested it yet. I don't recall ever seeing extractor marks on factory ammo. Is this common? Am I reading too much into it?
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  #2  
Old 11-27-2013, 08:20 PM
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Re: Pressure Signs

I tend to evaluate similar to you - primer watching can be fickle at best. Marks on the brass and sticky bolts are a no-go area for me.

I think it is weird to see extractor marks on factory ammo, but I have shot some factory fodder that I know is hot. They are more interested in velocity claims than brass life, that is for sure. Bottom line, I wouldn't use your experience with that factory ammo as any type of benchmark for your own loading.

I am a "never exceed book max" kind of guy. If you are at book max with your current load MHO is why push it? The extra velocity is probably worthless by any practical measure.... I know other guys view it differently but to me it is pretty simple risk vs benefit.

I would be interested in what the manufacturer would say if you emailed a pic and asked their opinion? Just curiosity on my part.
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Old 11-27-2013, 09:19 PM
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Re: Pressure Signs

I agree about max with the exception the COAL used combined with primer brands can vary pressures enough that book max is not max. Then again you can see pressures well below. My 6.5 is 1.5 below and on the edge.
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Old 11-27-2013, 09:40 PM
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Re: Pressure Signs

Quote:
Originally Posted by BrentM View Post
I agree about max with the exception the COAL used combined with primer brands can vary pressures enough that book max is not max. Then again you can see pressures well below. My 6.5 is 1.5 below and on the edge.
Totally agree with your entire statement above. As far as what i put in bold, my deal is that lacking a quantitative way to measure pressure, I stop at book max unless I see qualitative pressure signs prior. Not saying my way is the right way, but it gives me a comfort level.

I am afraid of "invisible pressure" if such a thing exists - I have a feeling it does as I have seen Lapua brass eat some loads that I wouldn't be comfortable shooting and look no worse for wear. I doubt it is truly unsafe in modern rifles, but my ignorance of what these limits are keeps me following the book.

How bad are the extractor marks on that factory brass? Any chance you put it on a chrony?

Last edited by varmintH8R; 11-27-2013 at 09:42 PM. Reason: Dang iPhone
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  #5  
Old 11-27-2013, 11:51 PM
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Re: Pressure Signs

Very faint actually. I only had the two rounds. The kid who owns the rifle shot the rest.

I could measure the head space too. Not sure about this poi brass. Looks decent enough.
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  #6  
Old 11-28-2013, 07:18 PM
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Re: Pressure Signs

IMO

Primer flattening is a function of headspace and not pressure

Extractor wipe marks can show up on soft brass or some other reason on a load that is safe. Change brass manufacturer

Sticky bolt lift is almost always a good sign of pressure

Ultimate pressure test is primer pockets holding primers on reloads
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  #7  
Old 11-29-2013, 10:59 PM
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Re: Pressure Signs

I would agree except I can take a bran new piece of lapau brass and get the exact same result. For example new brass is 1.832 and hs for my rifle is 1.840. I bump the shoulder back to 1.838. With the exact same load in fire formed and new the primer and extractor mark are very similar.

Accuracy is much better with proper hs though. I was having a newly developed issue which is why I tested all this stuff. Perhaps it is just coincidental.
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