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Twist Rate???

 
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  #8  
Old 04-01-2009, 06:29 PM
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Re: Twist Rate???

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.
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  #9  
Old 04-02-2009, 08:33 AM
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Re: Twist Rate???

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
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  #10  
Old 04-02-2009, 07:05 PM
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Re: Twist Rate???

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
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  #11  
Old 04-02-2009, 07:22 PM
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Re: Twist Rate???

Quote:
Originally Posted by BountyHunter View Post
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
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.
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  #12  
Old 04-02-2009, 07:25 PM
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Re: Twist Rate???

Please give us the formulas.

Steve
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  #13  
Old 04-02-2009, 07:28 PM
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Re: Twist Rate???

Quote:
Originally Posted by RockyMtnMT View Post
Please give us the formulas.

Steve

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!
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Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.

Last edited by Michael Eichele; 04-02-2009 at 07:33 PM.
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  #14  
Old 04-02-2009, 07:31 PM
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Re: Twist Rate???

Thank you.

Steve
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