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Twist Rate and stability

 
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  #1  
Old 12-16-2013, 03:43 PM
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Twist Rate and stability

Looking at Bergers site I play with this calculator. I have been wondering about my 204 bullets and how they match up. Current set up is under 1, which according to their info is not good enough.

How much stock do you put into this number?
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Old 12-16-2013, 04:06 PM
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Re: Twist Rate and stability

Sg at 1.0 means instant tumble
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Old 12-16-2013, 04:23 PM
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Re: Twist Rate and stability

Hmmm. Tell me what you think please.

3800 fps
1/12 twist
40 grain Vmax. Measures .75 tip to base.

Using those numbers at 30F and 4000 ft I get .93. I shot a 4 shot group at 500 yards that measured 2". I had 1 shot that I pulled another 2" left by accident. My finger was so cold I was playing with the trigger for feel and BANG. LOL
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Old 12-16-2013, 04:42 PM
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Re: Twist Rate and stability

I think with the small bullets variables like plastic tips become much more important. When I run the numbers for the 53 gr Vmax out of a measured 14" twist 22-250, it spits out a .86 Sg and they seem to stalize just fine out of my rifle.

I'm guessing the Berger calculator might be tweaked to reflect the stability of their cup and core HP VLD bullets.

There are a lot of variables in the stability formula such as specific gravity, length and shape of boat tail if any, length and shape of nose, specific gravity of the bullet, etc., that Berger doesn't include in the inputs.

The plastic tip alters the specific gravity of the bullet and also pushes the CG back
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Old 12-16-2013, 04:56 PM
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Re: Twist Rate and stability

If you measure the metal part of the bullet from base to where the tip starts I can give you a number that take a polymer tip into account , bet your in the 1.2 range though.
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Old 12-16-2013, 05:00 PM
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Re: Twist Rate and stability

Their system doesn't help or hinder their bullet line. It is just a plug and play unit that is not brand specific. I see your point about design etc though. I am sure more goes into a bullet design then I will ever understand. I just find it interesting that this bullet seems to fly just fine even though the computer says it should not

I was kind of thinking about trying the 55 grain 204 at .381 bc from Berger. If I can get it to fly around 3500 fps it will retain a boat load of energy compared to the lower BC 40 grain bullet. But when I look at the numbers of the stability issue I was unsure what to do.

It puts out as much energy at 700 yards as a 223 does at 400. I would shoot dogs at 400 with a 223 no problem.

Tinkering is fun. Just not sure what to think of the issue.
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Old 12-16-2013, 05:31 PM
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Re: Twist Rate and stability

Quote:
Originally Posted by BrentM View Post
Their system doesn't help or hinder their bullet line. It is just a plug and play unit that is not brand specific.
Not sure about this one way or another. I suspect it is "type" specific vs "brand" specific. I don't think it's intended to promote their line, but just an aid in determining the best bullet for your application and conditions
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