Thread: Fussy 243.

Originally Posted by Marty Henry

In the 1850s this was figured out by a bloke called green hill who came up with a formula to calculate the twist rate needed for any bullet length or alternately the longest bullet that will work with a given twist. It completely ignores weight . It also takes into account the projectile speed as as a bullet slows it's rotational speed slows and gyroscopic stability decreases. Which explains the occasional I'm on target at 100 yds but can't hit the target at 200. I know I've been there.

Actually the opposite is true, rpm degrades much less quickly than velocity....so bullets on the verge of stability wobble there way out untill velocity has dropped enough that the rpm will hold them stable.