NitroXAdministrator
(.700 member)
21/08/22 05:37 PM
Re: The Greenhill Formula for calculating barrel twist rate

Let's try it.

A Woodleigh .333 300 gr SP. 1.459".


T= (150 x D)/R

Where:
T- is the twist required (number of inches per one revolution)
D- is the diameter of the bullet (in inches)
R- is the ratio of bullet length to bullet diameter (length divided by diameter)

(150x.333)/(1.459/.333)=11.4"

If it is resized to .330 = 49.5/4.4212 = 11.2"
assuming no additional length.

A .330 250 gr resized to .323" bore:

1.302" 250gr SP .330 = 48.45/4.0310 = 11.24"
1.419" 250gr FMJ .330 = 48.45/4.3932 = 11.03"
i.e. for resized to a .323 bore.



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