Twist rate and bullet weight

[nivlac1960]

What is the correlation between twist rate and bullet weight? Is it the faster the twist rate the heavier the bullet or is it the faster the twist rate the lighter the bullet?

 

[casper]

Faster for heavier.

 

[Widude]

There is also info on line,(maybe Shilen) that has data for optimum twist rate for different calibers & different weight(length) bullets. Then if you go with an all copper bullet, they are longer when of the same weight.

Bullet length is the determining factor, usually going hand in hand with weight though. Most rifles are optimized for commonly used bullets with that round. It is worth consideration though when buying a rifle or rebarreling.

I had a detailed conversation with a gunsmith years back when I chose a twist rate for a custom 22-250. My expected bullet was a 50 grn for prairie dogging. I had considered faster, but he really favored the 1/14" common twist for that bullet. I went with his advice.

 

[n8dawg6]

faster for heavier is right. I have recently dealt with this in a two .308's. savage builds their .308's with a 1-10" twist, remington for the most part uses 1-12". i started out with the savage and couldn't get anything to work until i went to a boattail bullet, 165 g and up. even with a 165 or 168 g bullet, it still shoots better when i slow it down a little. the shape of the bullet matters too. higher BC bullets seem to need more twist to stabilize than lower BC bullets.

my remington, on the other hand, shoots anything 168g and less like a house on fire. it is much less picky. go over 168, though, and it doesn't like them.

 

[ardesa]

I have been told many times its not weight that is important but bullet length, some how to me the length would change the weight, or am I missing something?

 

[GM54-120]

Twist rate calculators
http://www.bergerbullets.com/litz/TwistRuleAlt.php
http://kwk.us/twist.html
http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Its better to slightly over stabilize than under stabilize most bullets. Soft lead bullets might do better just above marginal stability. You don't want to spin them too fast.

 

[AJ]

Ardesa is totally correct. Just because a barrel will stabilize a xxx grain round nose does not mean it will stabilize an equal weight VLD bullet. Typically heavier means longer, but bullet composition (jacketed lead vs all copper) and bullet profile all play into the length to weight value. Also a higher velocity cartridge needs slightly less twist to stabilize the same bullet as a slower cartridge.