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Hank45
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rate of twist
Aug 18th, 2011 at 11:25am
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     will a 1 in 9 twist stabilize a 261 grain bullet in a 7mm barrel/ Thanks, Hank Smiley
  
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38_Cal
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Re: rate of twist
Reply #1 - Aug 18th, 2011 at 12:23pm
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If you go to Mountain Molds' website, (You need to Login or Register to view media files and links), and plug in the bullet weight in the 7mm design page, it shows that a 1-6" twist is needed for your 261 gr. bullet.  About the heaviest bullet that should work in a 9" twist would be in the 175 gr. range, according to their program.

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screwloosetc
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Re: rate of twist
Reply #2 - Aug 18th, 2011 at 1:01pm
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Hank
What is the source of the 261 gr. 7mm?   
Tom
  
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Hank45
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Re: rate of twist
Reply #3 - Aug 18th, 2011 at 8:38pm
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The weight was 137 gn after I cleaned the gunk of the bottom of the pan, thankf for your input Hank : Smiley
  
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BP
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Re: rate of twist
Reply #4 - Aug 18th, 2011 at 8:43pm
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Hmmm....where did I put those check weights for the electronic scale?     Wink

  
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screwloosetc
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Re: rate of twist
Reply #5 - Aug 18th, 2011 at 9:34pm
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1 in 10 is the twist you want for the 7mm. I know because it has been my favorite caliber through the years. What are you building?
Tom
  
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joeb33050
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Re: rate of twist
Reply #6 - Aug 19th, 2011 at 6:55am
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If I did the arithmetic correctly, a 7mm at .284" with 9"twist will stabilize a  200 grain bullet which is ~ 1.34" long.
A .284" bullet 1.1" long will need a minimum twist of 11".
Says Greenhill.
joe b.
  
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screwloosetc
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Re: rate of twist
Reply #7 - Aug 19th, 2011 at 7:40am
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Joe 
I don't think 200 gr. 7 mm bullets are available. 175 is the heaviest in a jacketed. 160 in the lyman sil. I have a variety of 7 mm stuff 10 twist stabelizes all of it.120 to 160 cast. 110 to 175 jacketed. The 10 twist has given me the most consistancy over the years. To answer Hanks question the 9 will stabalize his 137 but heavier will be better. 
The 10 does it all. 10 will also put the jacketed to the same point of impact.
This is not suposition but from 50 years of shooting all kinds of 7mm.
Early military rifles were fast twist  military load was 175 gr rn.
  
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