Barrel Twist vs. Bullets

[overbore]

Gentlemen,
The following is predicated upon my individual research and your comments and inputs are encouraged but the following chart is offered as a guide to finding the correct bullet candidate for your new .30 cal rifle or, per my suggestion, start with a known quality bullet then spec your new barrel to mate to the bullet.
Sea Level, NACA Standard Day and .30 cal only!!!

Berger 175gr 1.270" long .537BC Twist: 1-12
190gr 1.380" " .583BC Twist 1-12
210gr .631BC " 1-11

LAPUA 155Palma 1.237 " .508BC " 1-12
185gr 1.315 " .521BC " 1-12

SIERRA 155gr Palma 1.135" " .450BC 1-12
168gr 1.220" " .426BC 1-11
175gr 1.242" " .505BC 1-11
190gr 1.395" " .525BC 1-10
200gr 1.395 1-13
BIB 165grFB
187grFB 1.325" 1-11-13

Now, if you only know the planned MV and the bullet length:
LENGTHS <2,800fps TWISTS
1.178-1.264" 1-14
1.265-1.366" 1-13
1.367-1.484" 1-12
1.485-1.626" 1-11
>2,800fps
1.055-1.138" 1-13
1.139-1.237" 1-12
1.238-1.355" 1-11
1.356-1.497" 1-10"

The above twists in the range of 10-12 result in a Stability Factor,SF) of 1.3. Twists in the 13-14 range reduce SF down to 1.1 range,or Marginal Stability. SF of < 1.0 is NOt stabilized adn SF of > 1.5 is max or overstabilized, excessive spin rotation ).

Hope this is useful, Overbore

 

[sewwhat89]

It seems the last part with twist based on MV is backwards. If you increase your MV enough, you should need less twist not more as posted.

 

[aJR]

Hi Over Bore, i shoot the 187BIBs at 3350 fps in a 13 twist,1.325 after meplating), their great, also i have shot the 200 SMK in a 13 twist,1.395 after meplating) and they are definatly point 1st..Jr..Jeff Rogers.. The top group in the pic is was fired in testing at 551yds with 200Smks with the 1st load i pulled from from my hat, i went to the next registered match with this load and won, guess all 40 bullets were stable .............

Gentlemen,
The following is predicated upon my individual research and your comments and inputs are encouraged but the following chart is offered as a guide to finding the correct bullet candidate for your new .30 cal rifle or, per my suggestion, start with a known quality bullet then spec your new barrel to mate to the bullet.
Sea Level, NACA Standard Day and .30 cal only!!!

Berger 175gr 1.270" long .537BC Twist: 1-12
190gr 1.380" " .583BC Twist 1-12
210gr .631BC " 1-11

LAPUA 155Palma 1.237 " .508BC " 1-12
185gr 1.315 " .521BC " 1-12

SIERRA 155gr Palma 1.135" " .450BC 1-12
168gr 1.220" " .426BC 1-11
175gr 1.242" " .505BC 1-11
190gr 1.395" " .525BC 1-10

BIB 165grFB
187grFB

Now, if you only know the planned MV and the bullet length:
LENGTHS <2,800fps TWISTS
1.178-1.264" 1-14
1.265-1.366" 1-13
1.367-1.484" 1-12
1.485-1.626" 1-11
>2,800fps
1.055-1.138" 1-13
1.139-1.237" 1-12
1.238-1.355" 1-11
1.356-1.497" 1-10"

Hope this is useful, Overbore