twist rate for a .300 RUM

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by tillroot1, Aug 23, 2008.

  1. tillroot1

    tillroot1 Well-Known Member

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    I am going to build a long range hunting rifle and would like opinions on twist rates to shoot 200 to 225 grain bullets. and opinions on barrel length as well. Thanks, Ron Tilley
     
  2. Varminator 911

    Varminator 911 Well-Known Member

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    Ron:

    Berger recommends an 11 twist for their 210. I don't know what Hornaday recommends for the 208 Amax. But unfortunately there aren't any/many really high bc 308 bullets like there are 7mm. At least there is nothing I know of from the major bullet makers that has the bc of the 7mm Berger 180 VLD.

    I'm hoping there will be soon. Right now there are Henson 180, 212, and 220. As I remember the 180 does fine in a 10 twist but not the 212. The 220 (bc~0.9) needs an 8 twist.

    I'm waiting to see if these bullets pan out. I don't think the current bullets that will work in an 11 twist do the 300 RUM justice. Run up what a 220 with 0.9 bc at 3000fps looks like on a ballistic program. Pretty impressive!! You could potentially get that from a 26 inch barrel and a gun below 10 lbs all up. That's what I'm hoping for.
     

  3. J E Custom

    J E Custom Well-Known Member

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    With the RUM,s velocity a 1 in 10 twist is whats recomended by
    Lilja and shilen for up to 250gr bullets. and a 1 in 12 for 180gr down.

    With standard 30 cal velocitys a 1 in 9 would be the way to go.

    J E CUSTOM
     
  4. jwp475

    jwp475 Well-Known Member

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    The Sierra 240 SMK has a .711 BC and Sierra recommends a 1 in 9 twist. A 1 in 10 twist will work with the 240 SMK's untill the range gets extreme...

    What is the BC for the Berger 180 VLD, is it highr than .711?
     
  5. remingtonman_25_06

    remingtonman_25_06 Well-Known Member

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    "At least there is nothing I know of from the major bullet makers that has the bc of the 7mm Berger 180 VLD."

    30 cal, 240g SMK .711 BC
    338 cal, 300g SMK .768 BC

    Is Sierra not a major bullet maker in your opinion??? Just curious as they both beat out the 7mm 180g VLD. If you didn't know, now you do. Thats the great thing about this site, you learn something new everyday!!

    BTW, JWP. Berger dont make a 30 cal 180g, they do make a 185g and its rated at .556 I believe. Nowhere near the 240g SMK at .711
     
  6. jwp475

    jwp475 Well-Known Member

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    I was asking about the 7mm 180 grainer, because of the post that you quoted, claiming that it is higher than any other major manufactors 30 bullets and I don't believe that is correct.
     
  7. remingtonman_25_06

    remingtonman_25_06 Well-Known Member

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    Oh I see now. The 7mm 180g VLD is rated at .684, which is still a little shy of the 2 big SMK's.
     
  8. Varminator 911

    Varminator 911 Well-Known Member

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    Hey guys you are right. But I just cann't get excited about the 240 SMK. Too heavy to launch with much speed even from the 300 RUM. Better to go with the Edge and a 300 SMK. Also, he was asking about bullets of 200 to 220, not 240.

    I think you will agree that in general the 308 bullets are less aggressively designed for bc than the 7mm. Compare Bergers or the JLK VLD bullets in 7mm vs 308. JLKs 7mm 180 has a bc of 0.735 due to an 18 caliber radius ogive. While the 308 210 has a bc of 0.665 due to a 15 caliber radius ogive. You can just look at their picture of the two bullets and see the difference.

    Would you agree with my assesement that the larger the caliber, the easier it is to build a high bc bullet? Just think of a 224 compared to a 510. The Hornady 510 caliber Amax has a bc of 1.05. You'll never do that in 224 or 243. So the 308 have gotten short shift on bc compared to 7mm.

    If I were building a 300 RUM, and I'm thinking about it, I'd certainly go no slower than a 10 twist. In fact I'd probably go an 8 or 9. Why, because one needs to shoot bullets that are high bc for their weight to really get a long range shooter. The Berger 210 will do just as well on wind drift as the 240 SMK because of it's higher speed. It is probably also more reliable on game. But you need both speed and high bc to get the best possible on wind drift.

    I'd probably go faster than 10 twist because I'd be hoping for better bullets in the 200-220 wt range that are longer and higher bc. Henson has them now, not proven but they're here. Even Berger will get around to this some day. I'd want to be prepared. But that's just me.

    Just my thoughts. Thanks for yours!!
     
    Last edited: Aug 24, 2008
  9. jwp475

    jwp475 Well-Known Member

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    JonA pushes the 240 SMKs near 3000 FPS out of his 300 RUM not exactly creeping IMHO. I'll agree the more agressive BC bullets with long olgivals can be finicky to get them to shoot small groups, YMMV.
     
    Last edited: Aug 24, 2008