Twist rate 8.5 or 9 "

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Iron Worker, Sep 12, 2010.

  1. Iron Worker

    Iron Worker Well-Known Member

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    Building a 7mm wsm I want to shoot 140gr to Berger 180 Gr VLD Berger says 9" twist will work with their 180 gr VLD. But other shooters use 8.5 " What difference does .5 make in that bullets flight ?
     
  2. dirtball

    dirtball Well-Known Member

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    My 7mm WSM has a 9 twist and shoots 180 Berger's just fine. The 8.5 will cost you a few FPS and will be harder on the bullets.
    Dave
     

  3. elkaholic

    elkaholic Well-Known Member

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    I would agree that a 9 twist is adequate for most shooting. I you were going to shoot at extreme ranges and use the 180's, you might want the 8 1/2 to stabilize the bullet better. This probably wouldn't be necessary at under 1000 yds.....Rich
     
  4. Iron Worker

    Iron Worker Well-Known Member

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    I won't be making any 1000 yd shots on game. My rifle was a Mod 70 Classic in 270 WSM with a Factory bbl that threw bullets once the bbl was hot. ( 3 shots and bbl was hot) I'm now having a Krieger 9"twist 26" #4 contour chambered in 7mmWSM installed. Rifle would of been ok for a once a season deer rifle. But I shoot all the time.
     
  5. Kevin Thomas

    Kevin Thomas Well-Known Member

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    Ironworker,

    The difference between a 1x9" and a 1x8.5" is virtually (and may be, literally) non-existent, depending on the method of manufacture. It's not at all uncommon for buttoned barrels to vary by a half inch either way, so that 9" twist could very well be an 8.5" in reality, or even a 9.5". Cut rifled barrels tend to be a good bit more consistent in this regard, but both methods can produce good barrels, and I'm not knockign the buttoned variety. My point is, given a minor difference like this, I'd tend to go with the faster. A bit of extra spin will very rarely cause you any problem, while not enough will be a major pain in the arse every time.

    Kevin Thomas
    Lapua USA
     
  6. aroshtr

    aroshtr Well-Known Member

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    I would go with the 9 twist. Not as hard on the bullets, a little less pressure, and still is plenty to get a 180 brger to fly well.

    aroshtr
     
  7. Iron Worker

    Iron Worker Well-Known Member

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    Barrel has been ordered. Its brux 9" twist cut rifled bbl. Brux had the shortest lead time of all the barrel makers