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The first sign of excessive pressure is...

 
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Old 05-28-2009, 03:04 PM
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The first sign of excessive pressure is...

...flattened primers? Then ejector marks? Then sticky bolt?

Just curious. I am working 7 mag loads and am already 1 grain hotter than the Berger manual and the primers look like they did before firing (with the exception of the firing pin dent of course).

Thanks.
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Old 05-28-2009, 03:18 PM
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Re: The first sign of excessive pressure is...

Do your case heads have rings on them? If they don't, the primers aren't flattened and your not having difficulty lifting the bolt, I would guess your ok.

But if your over what the manual says you can bet your getting real close...

Be aware that if you try to seat your bullets farther out touching the lands or let your brass necks get to long and it crimps the bullet when you close your bolt you could be in for a suprise. Either of these will cause a dramatic spike in pressure and since your already at the edge
there is no room for error. Keep a close eye on you brass neck length and bullet seating.
Best,

Dee
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Last edited by Seven Oaks; 05-28-2009 at 03:36 PM.
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Old 05-28-2009, 03:42 PM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by buckbrush View Post
...flattened primers? Then ejector marks? Then sticky bolt?

Just curious. I am working 7 mag loads and am already 1 grain hotter than the Berger manual and the primers look like they did before firing (with the exception of the firing pin dent of course).

Thanks.

I use velocity as the first sign of excessive pressure. You don't get velocity without pressure and higher pressure nearly always means higher velocity. If you shoot over a good Chronograph and keep the velocity in the expected range (and use appropriate powder/bullet combo's), you will stay in the safe zone.

Just remember, there aren't any 'magic' combinations that give super high velocities with low pressures. There is no free lunch.

AJ
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Old 05-28-2009, 03:53 PM
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Re: The first sign of excessive pressure is...

I use a blade micrometer . measure the case head before you fire and measure it again after you fire . it should be expanded about .0005 max . that's half of a thousandths . make sure to put the mic in the same location . I align the one blade up with the " 7 " on the head stamp . my 7 rem mag makes the federal primer look like a top hat with the minimum starting load , so I have used case head expansion for my pressure indicator . on the belted case I measure right on the belt . Jim
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Old 05-28-2009, 03:59 PM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by jimbires View Post
I use a blade micrometer . measure the case head before you fire and measure it again after you fire . it should be expanded about .0005 max . that's half of a thousandths . make sure to put the mic in the same location . I align the one blade up with the " 7 " on the head stamp . my 7 rem mag makes the federal primer look like a top hat with the minimum starting load , so I have used case head expansion for my pressure indicator . on the belted case I measure right on the belt . Jim
Jim,

In the past, I also used visual inpection of the brass, case head measurement and bolt lift/extraction as pressure signs. A couple years ago, I read an article about pressure and it changed my entire perspective on pressure/velocity and pressure signs. The author shows that from a statistical perspective, throwing a dart at a wall is about as good to indicate pressure as case head expansion is.

Here is a link to the paper.
http://www.shootingsoftware.com/ftp/...%2019%2004.pdf

I still monitor my brass and extraction, but I rely more on velocity. As long as I'm using an appropriate powder/bullet combination for the rifle, with published loads to compare velocities with; I trust the velocity I'm getting is a very good indicator that I am in a safe zone.
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Old 05-28-2009, 04:05 PM
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Re: The first sign of excessive pressure is...

AJ , I'll check the article out . I'm sure the measuring method , that I use , is not 100% . one flaw I see is , as the brass work hardens it will not expand as easily . thanks Jim
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Old 05-28-2009, 04:08 PM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by jimbires View Post
AJ , I'll check the article out . I'm sure the measuring method , that I use , is not 100% . one flaw I see is , as the brass work hardens it will not expand as easily . thanks Jim

He discusses both measuring difficulties as well as brass hardening in the article. I was very impressed with the article and it changed the way I did things. I'll be interested to find out what your impression of the information is.

Take care,
AJ
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