VLD bullet stability from a 1:10 twist

[cooper_m22]

I am shooting 95gr Berger VLDs out of a 26" barelled Cooper M21, 6mm Remington with 1:10 twist. Velocity is about 3200 fps. I am getting excellent accuracy at 100 yds and no indication of bullet instability. Unfortunately, I don't have access to a facility that would allow for long range testing.

I know 1:10 is a bit slower that what Berger recommends for this bullet. If the bullet is stable out to 100 yds, is it safe to assume that it will remain stable at longer yardage; say 600 or so?

Thanks for your feedback.

 

[glo]

The Miller stability value is 1.218 which is marginal, but yes the bullet should stay stable as it slows down and is still supersonic.

 

[tunanut]

My 10 twist doesn't like 95's 1MOA; prefers 85',87, and 90 1/2MOA. It really hates 105's 3MOA.

 

[RonAKA]

One thing to remember is that a bullet loses horizontal velocity much faster than spin velocity. So bullets that are stable at the muzzle become more stable as they go down range. Strange things happen when they go subsonic, but you should still be supersonic at 600.

Here is a good tool that can estimate the spin required vs velocity. Also if you enter the twist you have in your gun, then it shows a graph of stability factor vs velocity. One caution in reading this though. Don't calculate down range velocity and then assume that is when the bullet goes unstable. This graph is for muzzle velocity where it is known exactly how much spin there is for the horizontal velocity. As above this changes as you go down range, as the ratio of spin to horizontal velocity increases.

http://www.border-barrels.com/barrel_twist.htm

The thing to watch a little closer on marginally stabilized bullets is temperature. I was at the range today in cool weather, and two bullets I had thought were kind of OK, tripled in group size. Temperature had dropped by about 20 degrees. The program at the link above indicated I had a stability factor of 1.02 in one bullet, and 0.95 in the other at today's temperature.

 

[15Tango]

Ohhhhh, you're covered.

http://bulletin.accurateshooter.com/2010/11/berger-introduces-new-87gr-6mm-vld-for-110-twist-barrels/

Wayne