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Posted: 2/11/2006 5:20:05 PM EDT
I have read here, and in several other forums questions regarding what rifle twist for a given bullet. I have built serval guns and when choosing a barrel the first question I ask is what bullet are you going to use and build the gun accordingly.

The is a simple methol in choosing the twist developed by Sir Alfred G. Greenhill. The Greenhill formula is found in the British Texbook of Small Arms, 1929.

Its quite simple:

The twist required = 150/the lenth of the bullet in calibers times the diameter of the bullet

Or 150/(lenth/cal)*cal=twist required

Example: Take a 190 gr sierra hpbt in .308
the lenth of the 190 is 1.348
1.348/.308=4.376
150/4.376 = 34.273
34.273/.308 = 10.556

Therefore we can use 10-11 in twist for this bullet

Link Posted: 2/12/2006 6:29:09 AM EDT
[Last Edit: 2/12/2006 6:35:07 AM EDT by M4Madness]

34.273/.308 = 10.556



Don't you mean 34.273 X .308 = 10.556?
Link Posted: 2/12/2006 6:57:45 AM EDT
Ooooop correct, thanks for catching the typo

34.273 X .308 = 10.556
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