Too much pressure?

Discussion in 'Reloading' started by land308, Jun 24, 2009.

  1. land308

    land308 Well-Known Member

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    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.
    [​IMG]


    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?
     
  2. trueblue

    trueblue Well-Known Member

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    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.
     

  3. EddieHarren

    EddieHarren Well-Known Member

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    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".
     
  4. Freebore

    Freebore Well-Known Member

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    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.
     
  5. J E Custom

    J E Custom Well-Known Member

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    +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
     
  6. Limbic

    Limbic Well-Known Member

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    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.:)
     
  7. land308

    land308 Well-Known Member

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    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
     
  8. larrywillis

    larrywillis Well-Known Member

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    land308 ........

    Your cases don't look too hot IF you worked up to that load slowly. Be aware that when you switch to a new can of powder your pressure can be very different. This is real important if you're shooting hot loads! I have seen this most often with Varget powder. This picture shows how you can SLOWLY (and safely) work up to hot loads - that are safe.

    [​IMG]

    If you want your loads to chamber and extract easily, it's best to measure your cases at the shoulder. Check out our website, and you'll see some reloading tools and Tech Tips that will help.

    - Innovative
    WWW.LARRYWILLIS.COM
     
  9. land308

    land308 Well-Known Member

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    Thanks Larry for the input.
    If I keep with this endeavor for my 308 I will probably have to start buying powder in the 8lb containers so I don't have to work up loads so often. I usually load for pure accuracy and end up with loads in the lower to mid velocities so I don't have to worry about variances in powder as much.
    I am going back out with some loads of imr 4064 tomorrow.

    Why would the third case from the right have more of a crater than the 4th with the flatter primer?
     
  10. larrywillis

    larrywillis Well-Known Member

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    The third case was fired in a different rifle. I selected those particular cases for the picture. The idea of that picture is to show shooters that increasing your loads "slowly" allows you to be on the safe side when you arrive at maximum pressure.

    I always try to get powder in 8 pound kegs. It goes quickly if you shoot a lot. 4064 is another very good powder (and quite similar to Varget), except it is more termerature sensitive. It's my second choice for 308 Win.

    - Innovative