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Old 03-31-2012 | 05:06 AM
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lemoyne
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There are a couple of things that can fine tune the twist. one is the exact caliber of the bullet the other is the velocity coming out of the muzzle.
I ran a few through the Greenhill program to demonstrate what I am talking about , and to deal with some misconceptions what regulates the twist is a combination of length and diameter weight has nothing to do with it but velocity does it is one of the controlling factors.
A .458 dia. bullet with a velocity of 1800 and a length of 1 inch is an exact match with a twist of 31 per inch.
a .450 dia. bullet at a velocity of 1800 with a length of 1 inch is an exact match with with 30 per inch.
a 430 dia. bullet with a velocity of 1800 is an exact match of 27 per inch
now if you increase the velocity it reduces the twist if you lower the velocity it requires a faster twist.
A 40 caliber bullet traveling 1800 fps 1 inch long exactly matches with a twist of 24 but a 40 caliber bullet 1 inch long traveling 2800 fps exactly matches a twist of 24.
One of the things you need to remember about this is that a bullet that is under stabilized will wobble and turn end over while a bullet that is over stabilized has a 15 % tolerance before it becomes unstable.
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