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

34.273/.308 = 10.556

Don't you mean 34.273 X .308 = 10.556?

Ooooop correct, thanks for catching the typo

34.273 X .308 = 10.556