Question that has me stumped....

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by The Oregonian, May 7, 2014.

  1. The Oregonian

    The Oregonian Well-Known Member

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    Been reading here for about a year...very knowledgeable folks, and I have learned more that I can describe.

    I thought I had a few concepts understood, but reading on the Nosler site has me a little confused. Any wisdom from the clan would be appreciated.

    The ballistics data for the 270 and 280 (not the AI), both shooting a 140gr AB. It lists the MV for the 270 at 2900 and the 280 at 3000. Why would the 280 be a fair amount faster, given that I think the 270 has a higher max chamber pressure in the SAAMI spec. I guess I had been assuming that they wouldn't be loaded to a different percentage of spec. Where is my understanding off (I assume Nosler doesn't have an error on their site)?

    Side note - my understanding is that the 280 spec pressure is lower due to being developed as a semi-auto and in bolt form the 280 should be able to handle pressures closer to the 270.
     
  2. FEENIX

    FEENIX Well-Known Member

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    Look at the barrel twist rates (and sometimes barrel length) on the test rifles; .270 Win is 1:10" and the .280 Rem is 1:9.5".
     
  3. Trever

    Trever Well-Known Member

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    Bearing surface?
     
  4. barnesuser28

    barnesuser28 Well-Known Member

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    From another thread posted my Michael Eichele

     
  5. angus-5024

    angus-5024 Well-Known Member

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    I believe that part is due to bearing surface (more friction with the longer .277 bullet) and the other is simply because there is more surface area for the gas to push on.
    so a .277 cal bullet has .0603" cubed and the .284 bullet has .0633" cubed to push against.
    That's my understanding of it any way:).
     
  6. J E Custom

    J E Custom Well-Known Member

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    Pressure is applied to the bullet in PSI (Pounds Per Square Inch) and with everything being equal
    the larger bore will normally produce more velocity Because there is more surface area to push against. (More Square inches).

    Bullet design (Bearing surface) and barrel rifling does have an effect on velocity. But again if everything is the same, the bigger bore will be faster.

    J E CUSTOM
     
  7. roninflag

    roninflag Well-Known Member

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    What Barnes quoted from Michael Eichele...... it has to do with bore diameter/ expansion ratio.
     
  8. roninflag

    roninflag Well-Known Member

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    you get 2900 fps with a 100 grain .243 ; get 3000 with a 100 grain in 257 bob. same thing