Millers Twist Rule

I am attempting to learn more on casting bullets and I came accross this formula “Millers twist rule” which is on a excel spreed sheet.

As an example I been trying to find some bullets for the Benjamin Bulldog 357 but when I put in some possible figures to what Crosman has been using… well what I get is way off for the twist rate that they have in the gun which is (1:14″)

Has anyone used this formula before and if so is it any good?

http://accurateshooter.net/Blog/millerformula.xls

another formula for twist rate: Twist Rate = 3.5 * Velocity to the .05 * Diameter to the 2 / Length

ronin001

Participant

February 26, 2015 at 3:02 am

Caliber 0.357 Inches
Bullet Weight 145 Grains
Bullet Length 0.75 Inches***
Barrel Twist 14 Inches/turn
muzzle velocity 800 fps
Temperature 80 degrees Fahrenheit (59 is standard)
Pressure 29.92 inches of mercury (29.92 is standard)

Sg = 3.75 Over stabilized bullet???

Sg shouldn’t be less than 1.4. If Sg is greater 2 than or 4.0(largebore ), you may
gain some accuracy by going to a slower twist barrel.

**** not sure of lenght for this round

All Replies