240g Sierra bullet in a 1-12 twist barrel

Discussion in 'Reloading' started by texasdave, Aug 20, 2009.

  1. texasdave

    texasdave Well-Known Member

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    I have a 30-338 lapua that I am working up a load using the 240G Sierra bullet. I have been using IMR7828 and am getting 2800 to 2850 FPS out of it but it is a good news bad news scenario the good news is its on the paper the bad news is its all over the paper. It probably has a 6" spread. The bullet also looks like it is either tumbling or wobbling as it does not cut a clean smooth round hole. My question is am I running this bullet through a barrel that is putting too much spin? What are thoughts to correct this.
    I do not have the bullet right up in the lands and maybe that is part of the problem but my first thought was am I asking something out of the barrel its not designed to do.
    All suggestions are greatly appreciated.
    Thanks
     
  2. jmden

    jmden Well-Known Member

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    I think that's too slow a twist. Sierra reccomends a 9 twist. I shoot a 300RUM with 10 twist at about 3k fps MV. Acc'd to Litz/Miller equations it has a stability factory of 1.62, so should be OK at this rate. I'm guessing a 12 twist is not going to stabilize it. You need a faster spin rate. Good luck.
     

  3. Michael Eichele

    Michael Eichele Well-Known Member

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    +1

    Your stuck with no heavier than a 210. The 12x isnt optimum with the 210's but will work. 180-200's would be better for the 12x.
     
  4. BountyHunter

    BountyHunter Writers Guild

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    You are running too slow a twist first off as everyone has said.

    However, with the 240 in a 30-338, you should have been able to be closer to 3000 fps also (if your barrel was at least 28") which would help in the stability area with the faster rpm

    300 WSMs can easily run 210s in 1-11 and even shot sub 4" groups (at 1000) in 1-12s at close to 3000 fps so you are not far off.

    You can easily run 210s or 220s with a 1-12 if you are closer to the 3000 fps, but I would go to H1000, MRP, MRP2 or Retumbo. MRP and MRP2 has shown an ability to be able to give more fps in the large cases.

    BH
     
  5. jmden

    jmden Well-Known Member

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    Even with the higher RPM, he's just not going to stabilize that bullet in a 1:12. After reading Litz's book, it's much more clear that RPM increase helps stabilization, but very little--much less than I would've thought.

    Basically, don't depend on an increase in RPM to stabilize your bullet.

    I would think you'd be able to push that 240g faster than you are. Have you tried US869? I'm using 104.2 g (cool weather load) to push 'em just under 3K with a 26" barrel. Need another range session with good lighting conditions to confirm, but after treating with GunJuice, I seem to be getting about 50fps faster MV's.

    Good luck,

    Jon
     
  6. texasdave

    texasdave Well-Known Member

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    Thanks all for the replies. I have been shooting the 180's in it and they work great. I realized last time at the range it was a 12 twist so that was why I asked. Live and learn I guess. I think I can get the speed you guy's are speaking about but I wondered about stabilizing the bullet. I had thought about H50BMG powder too but the twist is still in the way.
    Thanks