Twist Rate???

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by AtownBcat, Apr 1, 2009.

  1. AtownBcat

    AtownBcat Well-Known Member

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    Hey guys i'm going to have to let Kreiger know something today about the twist rate for the barrell they are making. I had originaly decided to go with a 1 to 11 because i was going to shoot factory ammo(and i shot the 180g winchester silver tip). Well i have already bought the stuff i will need to start hand loading. It seems that most of you guys are using 200gr bullets in your 300 WM. I'm a little worried that 1 in 11 may not be fast enough if i go wth a 200gr accubond or a 208 A-MAX..on the flip side i could load some 165 grain stuff and that would be nice, but it seems that most here and on snipershide will go weight over a few more FPS...If there is anyone out there with some ideas...this is not one that is an "easy do-over" It is a hunting rifle first but i will be shooting at 1000 yards(targets)


    Thanks
    Ryan
     
  2. MagMan

    MagMan Well-Known Member

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    I doubt you'll be able to tell which twist will shoot factory ammo better especially through a high quality aftermarket barrel.

    That said I think your best bet would be to change it to a 10 twist or even a 9.

    I'd rather be over twisted than under twisted.

    Targets are where it starts, next thing you know you'll be shooting animals out there. It's best to be prepared.
     

  3. Mikecr

    Mikecr Well-Known Member

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    Not to be a smart ass,,,
    What is the problem?
    What are you going to let Krieger know?

    I don't see why there would be an issue with 1:11 for 30cal bullets,, if thats your concern.
     
  4. Michael Eichele

    Michael Eichele Well-Known Member

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    11x will handle 200's 208's 210's and 220's. It will not handle the 240 SMK.

    I am not trying to be a smart a$$ either but over spinning a bullet WILL have less than desirable effects on LR shooting such as a sub par BC and extra spin drift. 11 is more than enough for up to 220's.

    If 180 grains was your max bullet weight then 12x would have been much better.
     
  5. AtownBcat

    AtownBcat Well-Known Member

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    The problem is...kreiger already takes about 16 weeks to build a barrel and they said that If I didn't want to add to that I needed to tell them if I wanted a different twist than the one I ordered(11). Like I stated I was worried that an 11 twist would not handle the bullets over 200gr. You don't have to be a smart ass :)
     
  6. MagMan

    MagMan Well-Known Member

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    Not to be argumentative but I've never noticed any loss of BC or excessive SD with overly spun bullets. Actually I've shot some of my best groups ever (at 1k) with extreme RPM's. My BC's were on par or slightly above Nosler, Sierra and Berger's listings.

    Also my brother shoots a 300 AX with an 8 twist. It shoots the 240 SMK's spot on to Sierra's BC calculations with no noticeable spin drift, well no more than one could judge at 1K.

    Another one would be the 6mm-06 shooting the 107 SMK's @ 3400+ in a 8 twist, although I know this is not an extreme case scenario. Still no problems with that out to 1000 yards.
     
  7. Michael Eichele

    Michael Eichele Well-Known Member

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    I believe you.

    I would be willing to bet that if you used a 10x in the 300 AX next to your 8x you would see a notable increase in BC provided the bore quality and groove type were the same.
     
  8. 338 LEGEND

    338 LEGEND Well-Known Member

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    Go with the 10 twist it should handle all bullet sizes,spin drift from 10 twist to 11 twist is nell to nothing at a 1000.
     
  9. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    I understand your dilemma, this is always a difficult decision. I think the 1-10 is probably a good twist for trying to shoot the heavies well, and still work for the 160g to 180g bullets.

    The only food for thought that I will throw in is that as mono metal bullets become more prevalent, they tend to need more twist. On that note, I don't think you should go less than 1-10.

    Steve
     
  10. BountyHunter

    BountyHunter Writers Guild

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    1-11s in the 300 WSM are setting the house afire all the time with 210s

    Only reason seirra lists the 240 at 1-9 is because it was developed for LR NRA shooters (actually Army MTU tested them) shooting med velocity as a replacement for the old 250 years ago. They needed the extra twist for the lower velocities. Step up the MV and shoots great in 1-10.

    187 grainers are being shot in record groups out of 1-13 and 1-14 in the 300 Ack Imp all the time.

    Needed twist can be adjusted up or down by MV. 300 Weatheby has zero problems hammering 240s in little tight groups out of 1-10.

    Do not fall trap to assuming all 30 calibers shoot best with a 1-10, when in reality you have to be a little smarter than that and figure the expected MV into the equation.

    BH
     
  11. Michael Eichele

    Michael Eichele Well-Known Member

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    Very well put BH. As well as very true.

    I might add that many shooters still use the greenhill formula for twist calculations. Today there are so many more ways to calculate twist taking into concideration ALL the variables that go into finding optimum twist. There is much more to it than just bullet length and bore diameter which is primarily what GH was founded on using only two velocity ranges. No need to restrict ourselves today with all the knowledge and technology we have at our disposal.
     
  12. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    Please give us the formulas.

    Steve
     
  13. Michael Eichele

    Michael Eichele Well-Known Member

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    One such can be downloaded from the link here -------> Lilja Precision Rifle Barrels - Computer Software You will find it in the "bullet design calculation program". Input the values of your bullet and velocities and it will give you an optimum twist.

    Another resource can be found here -----------> http://www.eskimo.com/~jbm/cgi-bin/jbmdrag-5.0.cgi In this set you can change your twist until you find a stabilty factor of 1.5 at your velocity range.

    Have fun! :)
     
    Last edited: Apr 2, 2009
  14. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    Thank you.

    Steve