Bullet stability

[Jamie D Van Roekel]

Is it possible to over stabilize a bullet. I’m looking at building 3 different caliber rifles. For two of them I plan on using light for caliber bullets. Should I go to a slower twist to get the best results.

Any input would be appreciated.

 

[Inline6]

Depends on the bullets and speed. Yes you can over spin bullets to the point they come apart not making it to the target.

I rather a faster twist barrel myself, it gives me more options.

FWIW

 

[BourbonTrail]

It is possible to “overstabilize” a bullet.
However, that’s not really the issue. The issue is that the spin of the bullet results in a slow mode coning drift that grows with range. Due to the fact that the bullet decelerates longitudinally faster than spin decelerates , it creates an increasing dynamic instability resulting in drift. The faster the spin, the more the drift. Key is to only spin as fast as your heaviest bullet requires, otherwise risk unnecessary inaccuracies at range (400+ yards)

 

[Inline6]

It is possible to “overstabilize” a bullet.
However, that’s not really the issue. The issue is that the spin of the bullet results in a slow mode coning drift that grows with range. Due to the fact that the bullet decelerates longitudinally faster than spin decelerates , it creates an increasing dynamic instability resulting in drift. The faster the spin, the more the drift. Key is to only spin as fast as your heaviest bullet requires, otherwise risk unnecessary inaccuracies at range (400+ yards)

I'm not saying you are wrong, I personally have not witnessed this happen. On a slow twist barrel on the other hand I have.

There is a reason for the military choosing to go with a 1-7 twist vs a slower twist rates on the 5.56 platforms. The 55gr bullets would stabilize in a 1-12, because of tracers and M855 (62gr) that would not stabilize in a 1-12. They chose a 1-7, where a 1-10 maybe 1-9 would have probably been fine. I have made hits out to 650 yards with a 1-7, 16" barrel using 55gr ball ammo.

A friend had a 700 rem in 223, very accurate rifle, along as the bullets were lighter than 68grs. Talking about under 1/4MOA. As soon as you stepped up to 69gr bullets...you could not hit the target. Crazy to say the least, I had to shoot the rifle myself because I thought he was pulling my leg.

YMMV

 

[BourbonTrail]

The effect is by no means huge, but if one is splitting hairs, it’s worth considering. However, under-stabilized bullets are far more errant.

Robert L. McCoy’s Modern Exterior Ballistics

 

[Inline6]

I am sure that author is more intelligent than I. The 168 Sierra's are not known for accuracy past 600 yards mark.

I can only give my personal experience, shooting the load with my rifles with a 1-11.25 and one with a 1-10, they both shot well. 1-10 (24") was an AR platform was shooting between 1/2 and 3/4 moa at 900 yards. The other was a 1-11.25 (23") was a bolt gun. Again 1/2 to 3/4 moa at 900. I had a different barrel on my AI at the time 308 1-10 24" I was shooting 155s out of it at 2993fps, that gun was a little better than 1/2moa.

I don't know all I would like about ballistics, I have been fortunate enough to have put a fair amount of rounds down range. If a 308 was what one was using a 155 or 175, 185 would be better than a 168 Sierra. The 168 Hornady I had better results.

 

[TMac]

My sense is you can’t over “stabilize” a bullet. You sure can send one at too many rpm’s, creating issues, but that is not over stabilizing, it might be over spinning. But think about it, is it possible to be too stable? Don’t think so. I know what folks mean when they say over stabilize, but that’s not really what is happening as far as I know. Too fast a twist can cause issues, over stabilization is not one, don’t even think it's possible, over stabilizing that is.

 

[Rimshot]

As long as the lighter bullet doesn't physically disintegrate (usually target bullets with thin jackets), you'll be fine with a too-fast twist, because the lower ballistic coefficient of the shorter bullet means you're not shooting it at ultra long range anyway. Any theoretically increased spin drift is more than offset by the wind deflection potential of the less aerodynamic bullet, so it's more of an academic than practical concern. There could be a minor effect of velocity as well, but to me not enough to make the other tradeoffs worth it.

Personally I go with the fastest twist available unless it's a really special circumstance, as this gives the most options and greatest versatility with bullet selection. A fast twist barrel will shoot short bullets just as well as one with a slower twist, but longer bullets will have a lower ballistic coefficient in a slow twist barrel and tumble if it's slower still.