New brass - different velocities than fire formed?

Discussion in 'Reloading' started by tlk, Jun 16, 2010.

  1. tlk

    tlk Well-Known Member

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    Lapua 30-06 brass, 4x shot, cleaned with ultrasonic cleaner (CLEAN inside), all the prep work done and all brass is exactly the same. Avg = 2952 fps.

    SAME brass, same lot, never fired, prepped the EXACT same way, avg = 2990 fps.

    What gives? Need some light here...


    Thanks.
     
  2. Mikecr

    Mikecr Well-Known Member

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    New brass has yet to blow out to fireformed dimensions. So it has less capacity.
    You put the same load in a smaller case and pressure goes up, velocity goes up.
     

  3. tlk

    tlk Well-Known Member

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    OK cool, thanks.

    The other conclusion there is that the bullet leaves before the brass fully expands to the chamber, correct?
     
  4. Mikecr

    Mikecr Well-Known Member

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    No reason to...
     
  5. tlk

    tlk Well-Known Member

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    Mike, I have NO idea how to read that last statement - can you explain?
     
  6. Mikecr

    Mikecr Well-Known Member

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    Enough of that powder is lit & reacting to it's confinement, before ANYTHING moves or changes, that the affect in discussion barely relates to further downstream timing.
    Yes the brass expands quickly, but much of the powder's burn rate has already been altered by it's tighter confinement. So unless something unusal downstream counters this, all will be influenced by it.

    Given this, it makes absolutely no sense to rely on brass that isn't fully fireformed & stable in dimensions. Atleast, not for LR accuracy..
    And you bring a good example, which is supporting of this position.

    To heal this, many FL size brass -everytime.
    This is rediculous in my view, as dimesions can be managed without all the side affects.
    Fireforming(2-3 reloads) followed by minimal sizing is good enough.
     
  7. Don Titus

    Don Titus Well-Known Member

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    I've been working up an elk load for this fall in my 300 Win Mag and have decided on 73 gr. H4831sc behind 190 ABLR's velocity is around 2850 in used brass. Recently I've been shooting this load in new Nosler brass and my velocity is off between 100 and 150 fps and accuracy is about 1.5" at 100 yards versus under 1" with used brass.

    I've talked with several knowledgeable reloaders at my gun club and they say it stands to reason since new case expansion will reduce pressure to some extent and therefore drive the bullet just a bit slower.

    I intend to use the once fired cases for my hunt.

    Any thoughts on this?

    Don
     
  8. Mikecr

    Mikecr Well-Known Member

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    This thread is over 4yrs old..
    The knowledgeable reloaders at your club are clueless..
     
  9. Don Titus

    Don Titus Well-Known Member

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    I'm going to the range today to see how the fire-formed brass performs compared to the new stuff.
     
  10. phorwath

    phorwath Well-Known Member

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    Nothing like cutting to the crux of the matter... :)
     
  11. phorwath

    phorwath Well-Known Member

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    What equipment are you using to measure MV?
     
  12. Don Titus

    Don Titus Well-Known Member

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    I'm using a Beta Shooting Chrony. 300 WM results are as follows:

    All loads are 73 gr. H4831sc and Nosler 190 ABLR-

    All shots are at 200 yds from the bench.

    Temp. 70 degrees, humidity 45%, wind 180 degrees @ 8 mph

    Remington 700 w/24" barrel

    3 - 5 shot strings as follows:

    New Nosler brass:

    1. WLRM primer:

    Coal= 3.640" (.0010" off lands)

    Lo 2718 Hi 2763 Avg. 2752 delta 44.70 SD 19.44
    Group = 1.75"

    2. Fed. 215M:

    Coal= 3.640"

    Lo 2869 Hi 3108 Avg. 2925 delta 238.7 SD 102.80
    Group = 1.75"

    3. Once fired Nosler brass:

    Fed215M:

    Coal= 3.645"

    Lo 2786 Hi 2865 Avg. 2812 delta 79.17 SD 32.28

    (This will be my elk load)

    I have no idea why the significant difference in velocity SD between loads 1 and 2, yet group size was almost identical and about the same proximity to the bull.

    Obviously, any of these loads are suitable for my hunting purposes but I'd really like to know what's going on.

    Any suggestions or insights would be appreciated.lightbulb
     
  13. phorwath

    phorwath Well-Known Member

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    Don,

    I asked about the equipment you were measuring MV with, because some chronograph brands and models have better reputations than others. Now I'm not pooh poohing your chronograph just for personal enjoyment, but that chronograph doesn't have a stellar reputation for producing accurate and repeatable velocity measurements.

    When I review your load #2 chronograph data and see an extreme spread (delta) of 238.7fps, and an SD of 102.8, I'm further convinced that your chronograph reported some bogus velocity data. I would totally dismiss the load 2 velocity data.

    I wouldn't spend much time analyzing the rest of your velocity data in any detailed, serious manner, solely based on the model chronograph you're using. You also obtained a fairly large delta for load 3 (but nowhere near as extreme as load 2).

    Beyond that, I will note that load 1 used WLRM primers and loads 2 & 3 used Fed 215M primers. Even if all other components, powder charges, and aspects of your loaded cartridges were identical, the use of different primers often yields different MVs. So that adds another variable, in addition to the use of the unfired and once fired Nosler cases. If you wanted to explore the affect that once fired cases versus virgin brass has on MV, you would really want to keep all other aspects of the loaded cartridges identical. Powder lots, seating depths, primers, powder charges, case and case neck preparation - everything else should be kept as constant as possible.

    Hope you get your elk!
     
    Last edited: Sep 12, 2014
  14. Don Titus

    Don Titus Well-Known Member

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    Thanks for your input...I think I'm going to stop playing with stuff and adjust my velocity estimate from 2900 (published) to 2850 fps and dial it into the Nikon "Spot On" ballistics calculator and adjust my scope accordingly. I've burned a lot of powder fooling with this stuff ... the old adage applies "you get what you paid for", in this case $120 for the Beta and seemly inconsistent readings. I am going to put in a new battery and only use it on overcast days which may help.

    BY THE WAY, I saw your 2005 thread regarding how you set up your chronograph to virtually eliminate inconsistency ...very impressive, but I'm not going there.

    Peace,

    Don