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  1. #11
    User
    Join Date
    Jul 2011
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    BFN Freestate
    Age
    45
    Posts
    12,144

    Default Re: Insight into Gyroscopic Bullet Stability and Velocity

    Quote Originally Posted by A-R View Post
    Gyroscopic stability actually increases a little as velocity increases, all else being equal. So no, your accuracy improvement is not related to gyroscopic stability. I have found that the 1:12" twist rate of my 375 H&H's barrel will stabilise a 270 gn flat nosed cast lead bullet at 1500 - 1700 fps just fine. It stabilises much longer bullets as well, but I have not calculated the gyroscopic stability factor (Sg) yet. For sufficient stability from normal rifle barrels, a minimum Sg value of 1,5 is recommended. For subsonic loads using relatively long bullets, I see that a higher Sg is preferred. Then there are the muzzle-loader shooters, who often go to a significantly lower Sg with very short conical style bullets.
    That is why I asked, it’s not possible to shoot that bullet at ANY speed and have it not being overly stabilized, at 1100 ft/s you will have a stupid high Sg already.

    Casting is one subject I have no personal experience in, but, if you ask me, stability could very well actually be the problem in this debate, just the reverse of what the OP asked about. Bullet skipping is in fact a lack of stability, not so? If you had a slower twist rate then it would be possible the bullet had a better chance of gripping with the same material that does not in a 1 in 12 twist. If you make the lead harder then you can give it a better chance of interacting with the grooves of the barrel.

    So the physical problem is the hardness of the alloy, but the result of the problem is a lack of gyroscopic stability, the very thing the OP asked about.

  2. #12
    User
    Join Date
    Apr 2019
    Location
    Cape Town
    Posts
    1,783

    Default Re: Insight into Gyroscopic Bullet Stability and Velocity

    One thing that is very clear from drag curves is that you need a lot less spin at sub-sonic velocities to stabilise projectiles. Couple that to the fact that the best performing ogive shape is eliptical, you can shoot very heavy projectiles with conventional barrels at sub-sonic velocities without fear of stripping lead in the rifling.

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