Bullet/Barrel Twist Rate Calculator

OldTurtle

OldTurtle

Moderator - Deceased
I was reading an article on another site and it mentioned the "Greenhill Formula" for determining the slowest twist rate for a given bullet.

When I did a search, I found a website that provides a downloadable calculator that will allow the plugging in of the general bullet speed, the diameter, and the length and it will give you the slowest twist rate for the bullet... /ubbthreads/images/graemlins/grinning-smiley-003.gif

Barrel Twist Rate Calculator

Hope this helps with those that have questions..
 
Sir Alfred Greenhill was a professor of advanced artillery officers at Woolrich Military Academy in England from 1876 to 1906.

His formula is based on the rule, "The twist required in calibers equals 150 divided by the length of the bullet in calibers."

To use, first divide the length of the bullet by it's caliber in inches. For example a .30 caliber bullet is .308 diameter, divide that into it's length, say 1.125 to obtain 3.65 calibers long. Divide the 3.65 into 150 to obtain 41.09, or one turn in 41.09 calibers. To change to inches, multiply the 41.09 by the diameter of the bullet in inches, which is .308. The answer is 12.655 or 1 turn in 12 5/8".
 
Professor Greenhill's readme file that comes with the download says the program will only run in Windows 98 but it runs just fine in Vista 64bit
 
Shilen has a chart on their website.

remember, the greenhill formula was developed for cannon projectiles. It gets very close,..but some shooters have "tweeked" the formula a bit to come up some closer numbers.
 
Quote:
when you plug in a berger 40gr in .204 it gives a 1in10 berger says 1in12 or faster which is right?



1/10 is in the 1/12 or faster range.

t/c223encore.
 


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