# Barrel twist

#### Taz

##### Member
Hey ya'll!

I need some info on barrel twists for 30 cal. JLK 190 & 210. I know the 10 twist is norm, but would the 11 twist be better?

G

#### Guest

##### Guest
Taz--
What cartridge /velocity are you using? CJ

#### Taz

##### Member
I am using the 300 wsm. Velocity - I'm guessing 2950 to 3050.

G

#### Guest

##### Guest
Taz -- I forgot to ask the bullet length, so try this formula--
(180 x bullet dia x bullet dia)/ bullet length = rate of spin. If your velocity is below 2800 fps, use 150 instead of 180 as your constant. CJ

#### Tim Behle

##### Well-Known Member
Chris,

What formula do you use to determine your first number ( 180 or 150 ) versus Velocity?

I was thinking that with the formula you gave, I might be able to reverse it when working up new loads. With a known twist, it might help me look for a specific window of velocity for best bullet performance. But I can't find how your beginning numbers relate to the bullets speed.

G

#### Guest

##### Guest
Tim-- Good Question-- I pulled it off of one of the ballistics sites and I don't remember which one. I'll try to find it and get back to you. I don't remember seeing the formula, just the numbers given as constants. I'll try to look it up tonight. Chris

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