Barrel twist effect on bullet

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by hjl, Jun 22, 2006.

  1. hjl

    hjl Well-Known Member

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    If you have a 30 inch barrel chambered for 7mm RUM with a 1-7 twist {to use 200 gn wildcat bullets one day}.
    What effect does the twist have on a 162 gn amax at 3200-3300 fps on accuracy & expansion on light game to 500 yards?
    What effect does the twist have on a 140 gn nozler bt @ 3500 fps on accuracy & expansion on light game to 500 yards?
    What effect does the twist have on a 120 gn nozler bt @3800-3900 fps on accuracy & expansion on light game to 500 yards?
    Thank you for your replys.
    Regards
    hjl
     
  2. Guest

    Guest Guest

    <font class="small">Code:</font><hr /><pre>
    Vel -- Twist ---- RPM
    ----------------------------

    3300 7 339,428
    3500 7 360,000
    3900 7 401,142
    </pre><hr />

    If you're a BR shooter, you want the slowest twist the stabilizes the bullet. For LRH it likely doesn't matter unless you spin the bullet so fast it explodes from the centripetal acceleration.

    Personally I wouldn't build a custom gun for shooting ULD/heavy pills just to burn out the barrel on vermin loads. That's why I have three 300 RUMS.

    If you want a BR pontification from the expert, take a look at BB on Twist
     

  3. Mikecr

    Mikecr Well-Known Member

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    I don't know how tough Nosler's are. But alot of longer range bullets come apart &gt;310Krpm. If they stay together, then they'll be fine.
     
  4. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    You will tear the A-Max bullets apart at around 3050 to 3100 fps in most cases with a 1-7 twist. At least that is the case with a Lilja 1-7 twist 3 groove.

    The Ballistic Tips will take it and accuracy will be good. Expansion will be violent to say the least. I have shot the 140 gr Accubonds to a solid 3700 fps in my 7mm AMs with good accuracy.

    I would recommend a 1-10 if this is the bullet you would want to use all the time, in fact a 1-12 would probably be even better.


    Your really playing with the RUM using bullets of 140 gr and lighter, you will see little advantage over some of the smaller 7mm magnums. Bullets in the 160 gr range and higher really make these big cases settle down and produce good consistancy.

    Just my opinion,

    Kirby Allen(50)
     
  5. davewilson

    davewilson Well-Known Member

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    hjl, i don't think you need a 7 twist even for the 200 wildcats. an 8 will be more than enough and a 9 will work 99% of the time.the problem with a 7 twist is most have a lilja 3 groove and that's just not enough rifling, in my opinion. a 5 or 6 groove would work better, especially if it's a canted land design. personally i think a 180 berger is a better bullet and a 9 twist will work best with the 160-180 gr bullet weights.i agree about the lighter weight bullets,just a waste of time with this cartridge.
     
  6. hjl

    hjl Well-Known Member

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    Thank you for your reply.
    If I want to use 120gn -180gn bullets I should get a 1-9 twist is this right?
    If I want to use a 200gn wildcat will the 1-9 twist work?
    Regards
    hjl
     
  7. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    In most cases yes it will work very well. With the velocity potential of your RUM you should not have a problem with a true 1-9 twist barrel.

    Kirby Allen(50)
     
  8. davewilson

    davewilson Well-Known Member

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    hjl, if you notice in Kirby's reply he said a "true" 9 twist barrel.translation is if you get a 9 twist,make sure you're getting a cut rifled barrel and not a button pulled if you intend to shoot the 200's
     
  9. NorthernSniper

    NorthernSniper Well-Known Member

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    What about 200gr Accubonds at 2900fps? I thought I would be good to go with the old standby 1/10 but after reading through some of this info I'm not really sure. /ubbthreads/images/graemlins/confused.gif
     
  10. davewilson

    davewilson Well-Known Member

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    NS, thought we were talking about 7mm bullets? a 160 gr is the biggest accubond.

    a 200 gr would be a 30 caliber and a 12 would work for them.