Signs of Pressure vs COAL Question

Discussion in 'Reloading' started by Shooter Fred, Aug 30, 2011.

  1. Shooter Fred

    Shooter Fred Well-Known Member

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    Hello all,

    I went to the range this morning and shot some new loads for my 300 RUM. I made a few adjustments to the OAL and the signs of pressure seemed to go away. I moved the bullet .012 closer to the lands than where I had it with my first test load (total overall length is 3.60" and 2.98" to ogive)...I thought making a longer COAL would have made my signs of pressure increase? For instance, I am not seeing any ejector marks now and virtually no flattening of the primer.

    The odd thing is my velocities are all consistently in line with what was shot in my first test batch.

    Can anyone comment if this is typical with the 300 RUM?
     
  2. Reloader222

    Reloader222 Well-Known Member

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    To increase the OAL would not have much increase in pressure for as long as you stay safe from the lands. One usually would look for the best grouping with batches of various OAL. Should you go too near to the lands (and specifically with maximum or near maximum loads) it is advisable to decrease the load and see what it does to the grouping. If there is no flattened primers I would say you are still on the safe side.
     

  3. Shooter Fred

    Shooter Fred Well-Known Member

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    Thanks Reloader...I guess I was just trying to ask if its normal to see pressure signs decrease while increasing the OAL? I am a long way from the lands as my 300 RUM has a long throat.

    The signs of pressure definitely decreased as there was no case that was hard to open the bolt after firing and there was no ejector marks and virtually no signs of primer flattening. Whereas when I fired the same load before there was definite signs of pressure (the only difference was a longer OAL).

    Also, does outside temp have anything to do with pressure signs? The temp was a good 15 degrees cooler this morning than last time I shot.

    Thanks,
    Fred
     
  4. Tikkamike

    Tikkamike Well-Known Member

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    What powder are you using? and yes the out side temp will affect pressure and you will see it on a max or near max load the most usually.
     
  5. Shooter Fred

    Shooter Fred Well-Known Member

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    I was using Retumbo and the load was 98.4 grains...last time I used 98 and 99 grains and both showed high pressure signs but this time with 98.4 it showed virtually no pressure signs.

    This makes me wonder if I should bump it back up to 99 grains because the cartridge actually shot the best with 99 grains of powder but the presssure signs were definitely there. But with cooler temps and longer OAL the pressure signs went away (at least with the 98.4 grain load).

    As you may know, I am just getting into reloading...this is a crazy world! So many variables.
     
  6. Tikkamike

    Tikkamike Well-Known Member

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    I have a 7mm that shoots 1 hole groups with over pressure loads of 160 AB's and IMR 4350 and when I bring it down to a safe load it shoots 1" groups. I reccomend testing your theory 1 or 2 more times try to prove it wrong. if it holds true I would leave it where its at because you are obviously right at the max. Then try adjusting your seating depth to increase accuracy. you may have to switch powders. Some times a combo just doesnt work out
     
  7. MTBULLET

    MTBULLET Well-Known Member

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    increase in oal changes interior case volume.
     
  8. Shooter Fred

    Shooter Fred Well-Known Member

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    Thanks for all the suggestions! I will load a few up towards the high end and see if with cooler temps and the new OAL the pressure subsides a bit.
     
  9. Loner

    Loner Well-Known Member

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    A longer coal should always decrease pressure until you reach the lands. The book
    coal is a minimum not a maximum. And without a non temp. sensitive powder you
    are flirting with disaster being right on the edge. Be careful in hot weather. I would
    think the temp had as much to do with it as the lengthened coal.
     
  10. Shooter Fred

    Shooter Fred Well-Known Member

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    This is good to know...I appreciate it. I agree with you that temp probably had a fair amount to do with this.

    Just an FYI...I just loaded up a few starting from 97.4 grains, then to 98.4 grains then to the max 99 grains, all with the lengthened COAL. I am going to shoot these tomorrow...I will report back on my findings.

    Wish me luck...it would be nice to finally get a combo nailed down!!!
     
  11. Shooter Fred

    Shooter Fred Well-Known Member

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    Ok...heres what I found

    The 99 grains of Retumbo with the new COAL did not produce the tight group it did without the lengthened COAL. The pressure signs were definitely less however there still was more than the 98.4 grain load.

    The 98.4 grains of Retumbo produced the best group with the lengthened COAL .729" center to center at 100 yards. This had virtually no pressure signs.

    The 97.4 grains of Retumbo produced virtually identical groups as yesterday.

    My question is, it seems that the 98.4 grains of Retumbo seems to show about the max pressure I am comfortable with and also the tightest group. Should I leave the group alone and use this combo or should I know mess with the COAL again? I need to be able to fit the catridge in my magazine box for hunting so I am limited with the length I am at now. I will only be able to shorten the load.

    What are your thoughts?

    Thanks,
    Fred
     
  12. Shooter Fred

    Shooter Fred Well-Known Member

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    Any Suggetstions?
     
  13. MSLRHunter

    MSLRHunter Well-Known Member

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    It depends on whether that is an acceptable group to you or not. Keep in mind that shortening coal may increase pressure again. Also, retumbo is fairly temp stable so the higher temp shouldn't have made that much difference. Have you tried H1000?
     
  14. Shooter Fred

    Shooter Fred Well-Known Member

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    I would really like to get this rifle shooting in the 1/2" range...I haven't tried any other powder yet as I have a big jug of Retumbo and its expensive to buy all this powder. However, I am considering different powder at this point.

    I am looking in the Nosler Reloading book as I am using Accubond 180gr. bullets and it lists H1000 as a realtively slow muzzle velocity. I was thinking of trying Magnum or RL 25...any experience with these or H1000 in a 300 RUM?

    Since I am new to reloading, I have another dumb question...does powder really make a difference as some people say Retumbo works great and others say they have to use a different powder. Just dont know why it would work in one persons rifle and not in mine?

    Thanks again!

    -Fred