Peterson/lapua brass volume

Discussion in 'Reloading Forum (All Calibers)' started by Borisserge, Mar 20, 2019.

  1. Borisserge

    Borisserge

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    I was wondering if anyone has first hand information on what difference of water volume there is between lapua 308 Palma small primer brass, and Peterson 308 small primer brass?
     
  2. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    Once the load is optimized for each case youll never know the difference- even if it was 3gr difference
     
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  3. divingin

    divingin Gold $$ Contributor

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    Dusty; I would assume he's wondering more about interchangeability between the brands.

    Unfortunately, I only have Peterson LRP 308. No Lapua at all.
     
  4. Uncle Ed

    Uncle Ed

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    For Optimal Performance You May Need To Change Your Load
    https://www.petersoncartridge.com/t...performance-you-may-need-to-change-your-load/

    [​IMG]


    A change in internal volume will change the performance of your load, and potentially your results at the target. The internal volume of Winchester casings is different than Hornady, which is different from Lapua, which is different than Norma, which is different from ours. This means that the load you worked up to use in Lapua casings, for example, might not be optimal for Peterson casings, and vice versa.

    The internal volume of Peterson casings is slightly less than some of the other casing manufacturers. This results in increased velocities. Once shooters re-work their load for optimal performance in our casings, they usually find they can achieve tighter groups than from the other casings they used. A common finding our customers report is, “Same gun, same bullet, cut my group size in half with Peterson casings.” But frequently this takes re-working their load.

    Along those lines Jack M. reported, “After reloading about 20 rounds of Peterson brass along with another manufacturer’s brass, we headed to the range. After a few shots we noted the Peterson rounds were consistently impacting about .75 to 1” higher than the other brass. Nice tight group, just higher. Confused by the difference, we set up our chronograph and found that using the same powder, bullet and die setting, we were constantly getting 90 to 100 fps more than with the other brass. The Peterson brass showed no evidence of overcharge. Nice surprise, more velocity without increasing the powder charge.”

    Another customer, Bryan J., had a similar story to tell. He reported that using the same load he used for our competitor’s casings, the results he got with Peterson cases were erratic. At first he thought maybe it was his gun. So he tried a second gun, with the same results. Now thinking it could be a difference in internal volume he worked up a new load for the Peterson cases. Then he got these results from 5-shot groups at 100 yards:

    • Competitor’s factory load = .89”
    • Competitor once-fired = .72”
    • Peterson brass out of the box = .44”
    The point of all this? Since rifle casings from different manufacturers have different internal volumes, you may need to change your load, to optimize your performance when using casings from a different manufacturer.
     
  5. mike06

    mike06 US ARMY 1970-1977 Silver $$ Contributor

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    For what it's worth I am now up to 30 firings with Peterson 308 SRP brass. I do anneal after each firing do a full resize with a Redding FL Bushing die. No splits and primer pockets are still holding stong.
     
  6. Ned Ludd

    Ned Ludd Silver $$ Contributor

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    From Ben Preston, Peterson Customer Support: "Also the h2o grain weight is 57.3 grains of water on average".

    In my hands, several different Lots of Lapua SRP .308 Win brass have had water capacities in the range of 55.6 gr to 56.1 gr, with most being close to 56.0 gr.
     
  7. Borisserge

    Borisserge

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    Thank you for all your wonderful information!
    This helps me with my planned project.
     
  8. greisdor

    greisdor Silver $$ Contributor

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    Question - what kind of water was used in measurement? Heavy water, mineral, distilled, salt ?

    Wouldn’t ml be better measure of volume?
     
  9. damoncali

    damoncali Gold $$ Contributor

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    It would, but how would you measure that?
     
  10. david kieffer

    david kieffer Gold $$ Contributor

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    I use a syringe with a 21 gauge needle , you can use the graduations on the syringe ,but my results are tighter using weight. however the syringe is very helpful with filling cases. hope this helps. dave
     
    Last edited: Mar 20, 2019
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  11. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    Heavy water? What yall doin up there i need to know about?
     
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  12. Ned Ludd

    Ned Ludd Silver $$ Contributor

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    I use plain tap water. It works. Pure water has a density of one gram per cubic centimeter at 4 degrees C. The minute amount of impurities in tap water and differences in temperature will change the density of water ever so slightly, but pure water at room temperature still has a density of approximately 0.999 g per cubic centimeter. In other words, the density is close enough to 1.0 gram per cubic centimeter that it will not normally be the limiting source of error in the measurement of case volume. For the same reason, we typically use the weight of water rather instead of volume because it is much easier for most people to accurately weigh empty versus filled cases, rather than trying to accurately measure water volumes in the range of a few milliliters.

    Per Dusty's observation, I would avoid the use of heavy water (D2O). It's very expensive, and the added density (1.105 g per cubic centimeter) makes case volume calculations more difficult than they need to be. ;)
     
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