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240 weatherby twist rate

 
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  #8  
Old 01-05-2013, 07:40 PM
Edd Edd is offline
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Re: 240 weatherby twist rate

When using 3000 fps as the baseline, the Berger stability calculator says you need an additional 3000 fps to compensate for the difference between an 8" and 9" twist.
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  #9  
Old 01-06-2013, 01:24 PM
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Re: 240 weatherby twist rate

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Originally Posted by Edd View Post
When using 3000 fps as the baseline, the Berger stability calculator says you need an additional 3000 fps to compensate for the difference between an 8" and 9" twist.
twice the fps eh.. had to wake up first on this one as I worked over-night last night

Bullet RPM = MV X 720/Twist Rate (in inches) so a 3000 fps bullet from an 8" twist is spinning 270,000 rpm

a 3300 fps bullet from a 9" twist is spinning 264,000 rpm, or less than 1% difference.

I'll dare you later to get a 105 in a 243 later to 3000 fps even , most likely would be 2900 to 2950, so you are actually talking fewer rpm from the slower cal. with the faster twist....

Last edited by Lefty7mmstw; 01-06-2013 at 02:15 PM.
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  #10  
Old 01-06-2013, 02:14 PM
Edd Edd is offline
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Re: 240 weatherby twist rate

78% more, not quite double.

Using the same Berger calculator.........

3300 fps in a 9" twist gives a stability factor of 1.24
2900 fps in an 8" twist gives a stability factor of 1.50

A minimum of 1.5 is recommended. Seems there may be more to it than RPM. Perhaps higher velocity makes a bullet more unstable.
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  #11  
Old 01-06-2013, 05:50 PM
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Re: 240 weatherby twist rate

Moosie, do you actually believe those books are assembled without "real world experience"?

Berger knows what they're talking about. Go with a 1x8", at a minimum. Dancing too close to the edge otherwise, and that's where the troubles begin.
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  #12  
Old 01-06-2013, 06:58 PM
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Re: 240 weatherby twist rate

Thanks for the input guys. I Know they recommending a certain twist for a certain bullet. I guess I should rephrase my question, if I go with a 1:8 twist will I be able to shoot both 105's and the 85, 87's with that twist? Or would 1:9 be better? It would be much simpler for me to just choose one bullet weight and build the gun for that one bullet weight, then I could just go by what the manuals recommend. But I really wanna twist that'll shoot both. So what twist will let me shoot both, accurately?
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  #13  
Old 01-06-2013, 09:00 PM
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Re: 240 weatherby twist rate

moosie,

You ALWAYS choose a twist based on the longest/heaviest bullets you plan on using. The lighter, shorter bullets will take care of themselves. You can spin a bullet faster than what's "needed" without any problem. You won't "overstabilize it" (no such thing), you'll merely have a higher Stability Factor than what's actually required to keep it nose on. Going the other way, with insufficient twist and too low an SG is likewise ALWAYS a problem.

My caution here is based on Berger's recommendations, and the fact that the scenarios they calculate their SGs on still have a few wildcards that can come up. I've mentioned before that buttoned barrels can easily (and routinely do) vary by as much as a half inch from their stated twist rate. Faster or slower, purely luck of the draw in the case of your particular barrel. I just like to have some edge for such little bugaboos . . . just in case.
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  #14  
Old 08-29-2013, 05:20 PM
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Re: 240 weatherby twist rate

Quote:
Originally Posted by Kevin Thomas View Post
moosie,

You ALWAYS choose a twist based on the longest/heaviest bullets you plan on using. The lighter, shorter bullets will take care of themselves. You can spin a bullet faster than what's "needed" without any problem. You won't "overstabilize it" (no such thing), you'll merely have a higher Stability Factor than what's actually required to keep it nose on. Going the other way, with insufficient twist and too low an SG is likewise ALWAYS a problem.
I suppose then, we only need to be concerned about, is what RPM they begin to disintegrate at.
Having absolutely no experience in this area, I'm curious if accuracy ever suffers at the extreme RPMs, assuming they don't disintegrate.
I have one 22-250 with a 1 in 14 twist and another with a 1 in 9 twist. I also have nearly 3000, 22 caliber bullets from many years ago when I had an FFL. They vary in weight from 50 gr to 63 gr. All being either Hornady or Sierra. The 50 gr Hornady SX, I can shoot in my 221 Fireball. I should be able to shoot the remainder in my new Savage LRPV with a 1in 9 twist. I assume the 52 & 53 grain Sierra HP will no blow up on exiting the barrel.

I apologize if this is too far off the path. I'll search for another thread if I am.

Spencer
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