new brass faster(fps) than necked brass

Discussion in 'Reloading' started by jorvin, Jun 12, 2011.

  1. jorvin

    jorvin Well-Known Member

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    i shot a 308 today and with new full sized brass i got 2760 fps. than i shot once fired neck sized brass (same load/bullet) and i got 2675 fps. is this because the new brass is expanding making higher pressures????
     
  2. Broz

    Broz Well-Known Member

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    Maybe because the barrel was warmer than at first? 15 fps is not a huge spread. What chronograph was used?

    Jeff
     

  3. jorvin

    jorvin Well-Known Member

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    spread was 65-70 fps. but you may have something there with barrel temp?
     
  4. Broz

    Broz Well-Known Member

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    Oops, sorry, my eyes did some number swaping for me there. I have seen swings like this as a barrel heats up, and also, if you have a shooting chrony as I do this is probably the norm .

    Jeff
     
  5. J E Custom

    J E Custom Well-Known Member

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    If you did not size the new brass before you loaded it, It sounds like there was more neck tension
    than on your reloads.

    You may want to look at a different expander ball on your dies(Smaller) to get more neck tension.

    Also if your chamber is a little larger than the new brass, after you fire form and neck size only
    the case has more volume (This will lower the pressure with the same powder charge).

    Just a couple of ideas to check out.

    J E CUSTOM
     
  6. Mikecr

    Mikecr Well-Known Member

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    It's because the new brass has not yet expanded to the volume of your fireformed -neck only sized brass. This is the reason for fully fireforming, and loading as you intend to, BEFORE attempting any load development with it.
    It's ok. You just can't expect much from 'brand new' brass.
     
  7. davkrat

    davkrat Well-Known Member

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    I like to shoot one of my plinker 110gr VMax loads in my new .308 brass to fireform them to my chamber and then neck size for my hunting loads. Seems the brass is more uniform after firing, sizing and trimming.

    I'm moving towards getting 20 or so pieces of brass that I weight sort and weigh bullets for as my primo hunting rounds and then don't do quite as much work on the rest of my practice rounds. Practice rounds get loaded until they're just dead and I don't care so much if I lose one.
     
  8. jorvin

    jorvin Well-Known Member

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    thanks guy's i'm thinking it's the new brass has less volume IE: higher pressure ,more fps. i'm going to work up my once fired brass for oct. in wyoming. thanks and good luck this year.
     
  9. texastrophy

    texastrophy Well-Known Member

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    What he said.