Home Forums Hunting & Shooting Ask The Gunwriters Twist vs Weight

If you replaced the lead core of a 150 grain bullet with tungsten, the bullet would have the same bearing surface but would weigh well over 200 grains. Would it need a faster twist to stabilize it instead of the 150 grain bullet?

Wayne

The RPM required to stabilize is a function of velocity, twist rate and bullet length
The velocity is a function of bullet weight and (simplified) case capacity.

So, if you increase the weight, you will be lowering the velocity. IF your origional 150gr was borderline stable, than you won't be stable at the 200gr velocity. On the flip side, if your 200gr velocity and twist rate can provide enough RPM's to stabilize that bullet length, than you will be OK.

Clear as mud?

No, allows a SLOWER minimum twist.
The minimum twist required to stabilize a certain caliber bullet is a function of: bullet length (longer needs faster twist), velocity (slower needs SLIGHTLY faster twist), bullet density (denser ex: tungsten allows slower twist, less dense ex: solid copper requires faster twist) and "medium" = air at sea level vs. air at 10,000 ft vs. water---that the bullet goes through (the denser the medium, the faster the twist required so less twist required at 10,000 ft. than at sea level)
joe brennan

Dunno. Since weight and length have pretty well gone hand in hand for so long, I'm not convinced that it is greater weight ( or length)that requires faster twist. Slower, you bet, because of the pressure thing. ?

Look at the twist rate recogmended for a VLD style bullet, vs the rate that you know works for a RN style of the same caliber and weight.

Weight and length only "go hand in hand" when your talking about the same basic style/construction. In the same caliber, a 200gr LWC will be a lot shorter than a aluminum 200gr VLD style, even though both weigh the same and can be launched at the same velocity, do you think they both have the same twist requirment?

Yes, it's the pressure thing that forces the lower velocity with the heavier bullet. This could be avoided, for purposes of discussion, by using different chamberings IE: 150gr in a 308 and 200gr in a 300Wby, to get the same velocity for each bullet at which time you would find that they both respond to the same twist rate.

Tailgunner is correct.........length of the bullet (and related is bearing surface) determines required minimum twist rates.

This is why monolithic bullets (Barnes X) sometime do not shoot well vs the same WEIGHT of a standard lead/copper bullet.

The monolithic bullet, being longer for a given weight can sometimes require a faster twist rate for best accuracy.

MM