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Too much pressure?

 
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  #1  
Old 06-24-2009, 01:18 AM
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Too much pressure?

I am working up a 178 amax load for my rem 700 vs in 308 win. This rifle has always seemed to prefer velocities at the low end of the spectrum. My most accurate loads are generally my starting loads. It seems like the more powder I put in, the larger the groups become. I am working up this load because I would like to work my way out to 1000 yards this summer. Up until now I have only shot at 700 yards and under.
These primers are cci200. load was 43 grains of varget. 2.832 col (to fit magazine)
The bold lift was not stiff and there are no extractor marks. I don't have a chrony so i don't know the velocity. I have always borrowed a buddies chrony for my drop charts. My ? is what are acceptable pressure signs when working up faster loads. Obviously the people getting near max velocities don't have perfectly rounded primers to show for it. What is you personal limit when it comes to pressure signs?
The cratering is not as bad as it showed up in the pictures. Just a tiny ridge you can feel with you fingernail.



The load I have been using for my long range shooting up to this point is a 165 sst traveling at 2400 fps with 38 grains Imr 4895. When I get the velocities up around 2600 fps for this load my groups go from 1/2-3/4 moa up to 1.5 moa. This seem to be typical for this rifle. Any suggestions?
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  #2  
Old 06-24-2009, 05:40 AM
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Re: Too much pressure?

land308,
Measure the base of the case ,ahead of the web, before and after firing. When you get 0.0045-0.005 of expansion, you are nearing max load. Just one more tool for finding max pressure, along with the other usual signs. I learned this from an experienced shooter on this site, so just passing it along.
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Old 06-24-2009, 06:07 AM
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Re: Too much pressure?

It is not unusual to get good groups at the low end, and then have groups open up some, as the powder charge is increased. Careful measuring, as described in the post above, should allow you to make small increases in the powder charge, until groups begin to tighten up again, as you approach the next "node".
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Old 06-24-2009, 08:14 AM
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Re: Too much pressure?

You definitely need to get a chrony! I use this along with bolt lift. If the bolt lift just gets a bit tight I'll back down and/or change powders to get a/my desired safe pressure/velocity. You need a chrony to measure SD and ES and the velocity you are trying to attain. Although groups do tell the picture. A primer change can make all the difference in the world when stretching out distances due to SD/ES.

Measuring cartridge base is a good indicator too, if you have the micrometer tools to do that.

Some cartridges do show pressure 'indicators' at bottom loading, this all relevant to a particular loading with all components coming into play.

Those 'ridges' on the primers could be 'primer flow' due to the firing pin diameter vs. bolt face firing pin hole. Maybe needs to be bushed.
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Old 06-24-2009, 09:01 AM
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Re: Too much pressure?

Quote:
Originally Posted by Freebore View Post
You definitely need to get a chrony! I use this along with bolt lift. If the bolt lift just gets a bit tight I'll back down and/or change powders to get a/my desired safe pressure/velocity. You need a chrony to measure SD and ES and the velocity you are trying to attain. Although groups do tell the picture. A primer change can make all the difference in the world when stretching out distances due to SD/ES.

Measuring cartridge base is a good indicator too, if you have the micrometer tools to do that.

Some cartridges do show pressure 'indicators' at bottom loading, this all relevant to a particular loading with all components coming into play.

Those 'ridges' on the primers could be 'primer flow' due to the firing pin diameter vs. bolt face firing pin hole. Maybe needs to be bushed.
+1
Primers are a good indicator as is bolt lift.

Some primers have a softer cup and the CCIs are softer than most and will show signs of
pressure before some others.

Normally the reason a group opens up is the Standard deviation is not good and a different powder primer combination is called for.

I would try one change at a time. Change the primer only and see if there is any difference.
Then change to a powder with the same approximate burn rate.

But I would highly recomend a chronograph because it will separate the groupies from
the rock stars.

J E CUSTOM
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  #6  
Old 06-24-2009, 07:43 PM
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Re: Too much pressure?

Every round I've ever fired through my Rem 700 has done the same thing. Factory, handload-hot, handload-weak, anything. The firing pin is much smaller than the hole that it rest in. When the pin stikes the primer and the explosion is started some of the primer flows back around the pin. As long as the edges of the cup are relatively smooth and not too sharp you are fine.

Just echoing what Freebore said.
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  #7  
Old 06-24-2009, 11:33 PM
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Re: Too much pressure?

Thanks for the suggestions. I went back out tonight and worked up to 43.5 grains of varget. I only fired 3 shots because on the 3rd the bolt lift was stiffer and there was a faint extractor mark. Group size was 1.3" at 100 yards. I also took out some loaded down to 39 grains. This was one grain lower than my starting load. Group sizes ranged form .6 to 1.0 ". I am going to have to get my own chrony to see where my velocities are at. Thanks again
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