Berger Bullet stability?

[edge]

A while back a member here sent me the Don Miller Stability Formula applet, thank you

If I go on the Berger website I see that 308155V requires a 14 twist barrel.

If I plug in the info on that bullet from the Berger website into the Don Miller program:
@40 degrees and 2900fps

The program shows a stability of only 1.09 and that it should really have a 12.4 twist for optimum stability.

I currently shoot a 14 twist and a bit faster MV with good accuracy but I am shooting in 60 degree temps!

I am a bit concerned about cold weather shooting with this setup now, should I be?
I may see temperatures into the single digits on occasion which will drop my velocity a bit and with high pressure I may be less than 1.00 according to the program!!!

I would assume that Berger anticipates all temperature extremes with their recommendation of 1:14 twist minimum, but............


edge.

 

[elkaholic]

Edge......contact Bryan Litz at Berger and he should be able to answer all your questions. By the time you get this, he may even have an answer on this forum as he is a sponser. Good luck.....Rich

 

[BryanLitz]

edge,

Sorry for not replying to your question sooner.

The Miller stability formula is based on 'nominal' projectiles that have 'nominal' shape and balance. If a bullet is too far away from ordinary in some way, it can cause the program to have some error.

The thing that's special about the 155 VLD is the large void in the nose. This will affect the balance/mass distribution in a way that is favorable for stability. In particular, the ratio of transverse to axial moments of inertia is lowered by the short core.

Rest assured that even though the Miller stability formula predicts instability for this bullet in cold climates, the bullet will be jut fine in the 1:14" twist.

When calculating the recommended twist rates Berger uses a different program that's more sophisticated (much less user friendly) to more accurately calculate the bullets stability requirements taking into account all the details of the bullets construction. The error in the Miller formula (when there is error) tends to be conservative which is good. It would indicate a faster twist than you necessarily need, so it will keep you out of trouble.

Hope this answers your question,
-Bryan

 

[edge]

Thanks to both of you

Bryan would that apply to plastic tipped bullets too, such as the Accubond, SST, and others?

Sorry to be a pest, but would the Accubond with the thick copper jacket and base be more or less stable if it had the identical shape as the Berger VLD?

Since I am being a pest, can you suggest a program that works well?

Thanks again for your replies.

edge.