Determing barell twist
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11-27-2012, 03:55 PM   #1
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Determing barell twist

I have this formula to determine best twist rate for bullet. TR= C* D2/lL
I used 150 for C used .224 for D2 and .790 for L

I keep getting 84 for answer what am I doing wrong? I'm wanting it for a .224

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11-27-2012, 05:10 PM   #2
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150 is that bullet weight because there is no 150 gr 224 bullet.

11-27-2012, 05:42 PM   #3
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I'd go here and use the revised formula.

A Calculator for Barrel Twist Rate
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11-27-2012, 05:57 PM   #4
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Ok didn't know that was the weight , I used 55 for the 150 and still not coming up with a
Right answer. Here's what I'm doing

TR =55 * .224(2) divided by .790

* = multiply. Don't have a multiply sign on keyboard.

I will use the revised one and see if r helps

Thanks

11-27-2012, 06:01 PM   #5
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Another question thanks for the equation why is bullet weight not in formula?!

11-27-2012, 06:06 PM   #6
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Quote:
 Originally Posted by Tenderribbs Another question thanks for the equation why is bullet weight not in formula?!
Because bullet length is what is important.
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11-27-2012, 06:11 PM   #7
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Quote:
 Originally Posted by The_Kid I'd go here and use the revised formula. A Calculator for Barrel Twist Rate
what does the SG stand for? showing a different value based on the bullet material.

11-27-2012, 06:15 PM   #8
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Quote:
 Originally Posted by axxe55 what does the SG stand for? showing a different value based on the bullet material.
From that page:
Quote:
 The classic equation is for solid, lead alloy bullets of specific gravity (SG) 10.9, and "when the density of the bullet is less than that of lead or the density of the resisting medium is greater than that of air, the spin should be increased as the square root of the ratio of the densities." As SG decreases, the gyroscopic inertia of the bullet decreases in proportion, and one needs to increase the spin to compensate.
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11-27-2012, 06:23 PM   #9
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Quote:
 Originally Posted by The_Kid From that page:
thanks. didn't read that far! was thinking it had something to do density.

how do you find the SG of a particular bullet? is this information readily available?

11-27-2012, 09:59 PM   #10
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Quote:
 Originally Posted by axxe55 thanks. didn't read that far! was thinking it had something to do density. how do you find the SG of a particular bullet? is this information readily available?
I've seen from 10.9 to 10.7 as the benchmark for jacketed bullets.
Another example of it being used; JBM Ballistics, Drag/Twist.

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