The Physics of Twist Rate and Bullet Weight?

[Mike Fontaine]

Hi All, Hope you all had a wonderful Christmas! Anyway, what is the final word on twist rate. What I mean is, for a given caliber is a fast wis rate (e.g. 1:9 vs. 1:12) designed for a "heavier" bullet? I just don't get it! I have, for example, a rem. 700 in 308 (1:12) and get near identical accuracy out at 300 yards with a 168g and 155g bullets. While I'm asking the question, I just bought a rem. 700 (1:9) in .223 with a 20" barrel. Anyone have any powder and bullet recommendations??? :grin: I look forward to any responses!
Mike

 

[JD338]

The longer the bullet, the faster the twist required to stabalize the bullet.

JD338

 

[Ol` Joe]

Try this (Greenhill formula) general formula if velocity is under 1800 fps. If the velocity is over 1800 fps sub 180 for the 150 figure.

Twist = 150 X D²/L

Where: D = bullet diameter in inches L= bullet length in inches

The formula isn`t exact but is very close for most purposes. Greenhill developed it for the military in, as I recall, the turn of the 19th century and it works best with lead core bullets.

 

[MattC]

Mike,

The first link is to a simple twist rate spreadsheet.
The second is to a more sophisticated bullet design spreadsheet.

http://www.nfa.ca/content/view/132/197/

http://www.riflebarrels.com/articles/bu ... design.htm

Cheers

 

[Mike Fontaine]

Thanks Guys!