Kernel
Member
221swede,
The simple Greenhill twist calculation is:
Twist Rate = 150 * (Bore Dia, in)^2 / (Bullet Length, in)
I use a modified version I call the Greenhill-Velocity twist calculation:
Twist Rate = ((0.0375 * Muzzle Velocity, fps) + 75) * (Bore Dia, in)^2 / (Bullet Length, in)
Basically, my equation modifies the constant, 150, accordingly to a linear equation dependent on velocity.
So, if we assume 2,400 fps and a 1.200" long bullet (how long is your bullet?), per simple Greenhill calculation the twist rate is 6.3. Per my Greenhill-Velocity equation the twist rate is 6.9.
The math says a 1:7 twist should stabilize your bullet based on velocity, and 1:6.5 based on the equation that does not use velocity. I think 1:7 would work fine. However, this is all theoretical. I would want to hear some real-world results from actual shooters. 1:6.5 might be better. The difference between 1:7 and 1:6.5 is pretty slight. But, I doubt a faster twist would hurt anything. When in doubt, most shooters (and gunsmiths) will opt for the faster twist.
The simple Greenhill twist calculation is:
Twist Rate = 150 * (Bore Dia, in)^2 / (Bullet Length, in)
I use a modified version I call the Greenhill-Velocity twist calculation:
Twist Rate = ((0.0375 * Muzzle Velocity, fps) + 75) * (Bore Dia, in)^2 / (Bullet Length, in)
Basically, my equation modifies the constant, 150, accordingly to a linear equation dependent on velocity.
So, if we assume 2,400 fps and a 1.200" long bullet (how long is your bullet?), per simple Greenhill calculation the twist rate is 6.3. Per my Greenhill-Velocity equation the twist rate is 6.9.
The math says a 1:7 twist should stabilize your bullet based on velocity, and 1:6.5 based on the equation that does not use velocity. I think 1:7 would work fine. However, this is all theoretical. I would want to hear some real-world results from actual shooters. 1:6.5 might be better. The difference between 1:7 and 1:6.5 is pretty slight. But, I doubt a faster twist would hurt anything. When in doubt, most shooters (and gunsmiths) will opt for the faster twist.