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Twist rate vs velocity

 
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  #8  
Old 05-21-2009, 05:51 PM
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Re: Twist rate vs velocity

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Originally Posted by 3006savage View Post
It does not seem based on all the responses like velocity is a consideration if one is on the fence trying to decide between two twist rates.
Now that is not the question you asked originally. You asked if there is a rule of thumb.

But to answer the last question, look at the 240 SMK, Sierra says you should have a 9 twist. Why? It was origianlly designed for 2600fps for NRA LR comp in the 30-338 and 300 Win which were the two LR comp calibers then.

Yet today we normally run the 240 in 10 twists at 2800-2900 with larger cases such as 300 Wthby and 300 ack imp and smokin groups. So is it twist, stability or what? I just know that you do not have to use a 9 twist for sure. I also know it does effect MV and pressure from what I have seen using a slower twist.

I have found that slower twists allow more MV with less pressure and absolutely no loss of accuracy out to 1000 for sure, but again very barrel dependent.

As for all the subtle questions you asked, the answers would only apply to that one barrel, chamber, twist throat combo and what is the significant impact. you could do all that testing but what does it get you that has real applications.

Barrels are like twin women, they may look alike and have same parents, but boy are they ever different.

To me that amount of endless testing is kind of like "pole vaulting over mouse turds". You can do it but so what?

BH
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  #9  
Old 05-22-2009, 04:46 AM
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Re: Twist rate vs velocity

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Originally Posted by 3006savage View Post
It does not seem based on all the responses like velocity is a consideration if one is on the fence trying to decide between two twist rates.
I think the best source of information on bullet/twist might be from who's barrel your going to use. I own afew rifles same caliber but use different barrels in using same loads I don't see a big velocity spread. I always work up my load first then chronograph it fun to compare and I limited how many bullets I'm going to try. 30-06 I use a Lilja 1/11 25" long barrel and Bartlein 1/11 5R barrel for other,270 use a Hart 1/10 other Lilja 1/10 and the 30-338mags use a 1/10 other 1/12 twist barrel. I've done the same thing with some of my varmit rifles.

All the barrels are alittle different but not that much maybe I just got lucky.
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  #10  
Old 05-22-2009, 10:49 AM
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Re: Twist rate vs velocity

I wouldnt say you got lucky. As long as youre using the right bullet for the twist, all is well. There also isnt alot of practical difference between a 10x and an 11x barrel.

A big, noticable difference would be using a 155 VLD or AMAX type bullet in a 9 or 10x barrel versus a 14x barrel. Now the difference here in accuracy AND velocity will be very noticable.
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Last edited by Michael Eichele; 05-22-2009 at 10:53 AM.
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  #11  
Old 05-22-2009, 02:57 PM
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Re: Twist rate vs velocity

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Originally Posted by Michael Eichele View Post
I wouldnt say you got lucky. As long as youre using the right bullet for the twist, all is well. There also isnt alot of practical difference between a 10x and an 11x barrel.

A big, noticable difference would be using a 155 VLD or AMAX type bullet in a 9 or 10x barrel versus a 14x barrel. Now the difference here in accuracy AND velocity will be very noticable.
I've been lucky in that I shot the HBR matches with a 308 using a 168gr Bruno FB bullets when I quit was using a 30x44 with 1/18 twist shooting BIB 112/118gr bullets.


I shot a Kreiger 1/10 twist in 30-06 and that barrel was alittle faster with the heavier bullets than the 1/11 twist barrels using the same loads. I've got a 1/13 twist Ratchet rifled 4 groove barrel from Shilen chamber in 30-06 that my 150/165gr bullet rifle.

Are you using a 1/14 twist with the bullets you mention?
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