Bullets and Barrel Twist? Help

Discussion in 'Reloading' started by brianwy77, Dec 4, 2009.

  1. brianwy77

    brianwy77 Member

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    Dec 10, 2008
    I have a 6x.284 winchester, 26" barrel 1 in 8" twist. I have been shooting Berger 105 Match Grade VLDS with great grouping.

    But I would like to try the Berger 6mm 115gr Match VLD bullets for a BC near .600. I was told that the 115gr bullets wouldn't stablize in my gun. The 105's are running about 3259 with a spread of maybe 14fps. Has any one tried the 115's or could some one tell me why they wouldn't stablize. I don't know much about barrel twist in referance to the Bullet!

    Thanks, Brian
     
    Last edited: Dec 4, 2009
  2. 358sta

    358sta Well-Known Member

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    According to Berger's website, the recommended twist rate for the 6mm 115 gr. VLD Target or Hunting version is 1-7". With your velocity potential I think they would stabilize just fine in your 1-7" twist barrel. Only way you are going to know for sure is to purchase a box of 100 and give them a try. Both versions also have the same BC of 0.545.
     

  3. paste

    paste Well-Known Member

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    according to bergers website the recomended twist for the 6mm 115 vld is a 1-7" twist.looks like your already good to go. try loading a few rounds and see what happens
     
  4. paste

    paste Well-Known Member

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    looks like 358 beat me by 2 minutes.I must peck at my key board pretty slow! lol:D:D
     
  5. brianwy77

    brianwy77 Member

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    I messed up guys my barrel is a 1 in 8" twist the bullets ask for a 1 in 7" twist.
     
  6. freelunch

    freelunch Active Member

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    Brian,
    You don't show a location, which would be helpful to answer your question.

    You can calculate your stability free online using the Miller Stability calculator at JBM.
    JBM - Calculations - Stability

    If your handle indicates you are in Wyoming, then don't use sea level. 29.92 is standard at sea level, but at 5000 altitude as in Colorado or Wyoming, the station pressure is 24.92 on a standard day. That bullet is 1.365" in length. Using 3000 fps as a guess, 8 twist, then...

    at sea level, 29.92, 59F, the stability is 1.241 (too low)
    at sea level, 29.92, 0F in winter worst case, stability is 1.100 (too low)
    at 5000 ft ASL, 24.92, 59F, the stability is 1.490 (good to go)
    at 5000 ft ASL, 24.92, 0F in winter worst case, the stability is 1.321 (marginal, probably OK)

    Berger's advice on 1 in 7 twist applies to those at or near sea level, and not in the High Plains at 5000 ft ASL. They are giving advice for worst case (seal level in the winter).
     
    Last edited: Dec 5, 2009
  7. brianwy77

    brianwy77 Member

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    Thanks for the heads up I check out that JBM Website and ran the numbers about any way you could and every thing comes out around 1.5. I am going to give them a shot.

    Thats why I love these forums a guy can go from not knowing much about ballistics to pretty solid in a shot time with some hard work.

    Thanks a bunch!
     
    Last edited: Dec 5, 2009
  8. dirtball

    dirtball Well-Known Member

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    I have a 240 Gibbs, Shilen 30" 8 twist, it loves 115 gr Berger's, pushing them out at about 3,230 fps.
    It takes a certain RPM to stabilize any given bullet and most of the "Twist Rates" given by the manufacturers are for nominal velocities, so when you are pushing them faster you can get away with a little less twist.
    Be warned that the "standard" Bergers don't like anything much above 3,300 fps, and when the throat starts to get a little rough even at 3,200 they some times blow up.
    Dave