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Thread: A new one on me

  1. #1

    A new one on me

    I decided to develop a 6.5x55 load a little further.

    As stated in a previous thread, I loaded in 0.2gn steps beyond my original (and precise) 46.5gn of N160 behind a H 129gn SST. All case, primer, crimp, COL etc details remain the same.

    46.7, 46.9 were OKish.

    47.1 showed smoky cases, extractor and ejector prints on the case head. The primers looked OK.

    47.3 was all normal, but a relatively large group.

    47.5 - 3/8" group, (2 in the same hole) and no case anomalies.

    What do you think - poor obturation at the 47.1 gn point?

    I would have stopped at the 47.1, but the pressure signs were light.
    Last edited by charadam; 08-05-2014 at 13:25. Reason: Oops - N160, NOT N140.
    "Nonsense! They couldn't hit an elephant at this dista.....................".

  2. #2
    Do you mean N160? I hope so because from the figs above, with N140 and a 129gn SST a roughish look indicates you're up to circa 80000psi which is way, way, way over for a 6.5*55 (by about 25000psi!!). Not surprised about pressure signs!!

  3. #3
    Quote Originally Posted by otbed View Post
    Do you mean N160? I hope so because from the figs above, with N140 and a 129gn SST a roughish look indicates you're up to circa 80000psi which is way, way, way over for a 6.5*55 (by about 25000psi!!). Not surprised about pressure signs!!

    Thank you! Post now corrected.
    "Nonsense! They couldn't hit an elephant at this dista.....................".

  4. #4
    I wonder just when will cotton onto the fact that looking at primers is a futile exercise for judging pressures. Imprints on brass means pressures are way too high or you have seriously annealed and softened cases.

  5. #5
    I thought my post was clear.

    Only the 47.1gn load showed the anomalous smoky exterior and extractor/ejector markings.

    The pressure signs (case head marking) were light so I felt justified in continuing with a 0.2gn increment. This was a good decision, as the anomalies disappeared at the next increment.

    I do not have seriously annealed and softened cases.

    But thank you for your input.
    Last edited by charadam; 09-05-2014 at 15:35.
    "Nonsense! They couldn't hit an elephant at this dista.....................".

  6. #6
    Charadam
    Is there any chance that you have some cases with more work hardening on some than the others? -- It's wise to consistently anneal all cases before this type of incremental test.

    Ian

  7. #7
    All cases are new Lapua.
    "Nonsense! They couldn't hit an elephant at this dista.....................".

  8. #8
    Did you check case headspace length of the new cases to check if they're right for your rifle & consistent?

    46.7, 46.9 - you say were ok ish - did they show any smoke deposits like the 47.1 ones?

    Can you repeat the trial with a chronograph to allow you to graph bullet velocity against charge weight?

    Ian

  9. #9
    All cases were FL resized in an RCBS die that I have used for 6 years and 2000+ rounds.

    Cases were also trimmed to nominal length.

    The 46.7 and 46.9 loads were smoke free. When I said they were OKish, I was referring to group size.

    All loads were chronographed and there were no velocity anomalies.
    "Nonsense! They couldn't hit an elephant at this dista.....................".

  10. #10
    Have to wonder if for people who have to chase the pressure limits as to if a Pressure Trace system would not be a good idea?

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