Re: Bullet stabilization question
Stabilization isn't directly about barrel length or load.
That it's a larger 'Ackley load' isn't enough factor to concern over.
And barrel length is not a direct matter in this, because regardless of it's length the twist rate is set at 1 turn per 10" of displacement. Do NOT think of stabilization in terms of RPMs because it fails more tests than Paris Hilton..
Now indirectly both barrel length and load can affect stabilization, due to the potential for ugly bullet release, that has to be overcome by twist rate.
If a 24" barrel is short for the load, you generate higher muzzle pressure(fireball), which slaps the back of a freely released bullet at angles(especially with boat tails). This acts like crown issues and it amplifies any crown issues.
A supersonic bullet is least gyroscopically stable right at the muzzle, so if your twist isn't high enough bad results are set in motion right there(no matter where you notice them).
If a bullet is unstable(Sg <1.0) it will tumble immediately even with perfect release.
Marginally stable(Sg >1.0 but <1.5) would not tumble unless something challenges that condition to a point of being insufficient(like jacket failure or dynamic instability). But stability varies with conditions other than twist rate(bad crown, hi air density), so being marginal has it's risks.
Fully stable(Sg ~1.5) gives you margin without hurting performance.
Using the Miller rule of thumb for stability(for illustration) and my measurements of a 95grVLD,
Sg = 1.36 @ 3kfps, 9tw, under ICAO conditions
Sg = 1.44 @ 3kfps, 9tw, @90deg
Sg = 1.28 @ 3kfps, 9tw, @30deg
Sg = 1.10 @ 3kfps, 10tw, under ICAO conditions [bad performance]
Sg = 1.17 @ 3kfps, 10tw, @90deg
Sg = 1.04 @ 3kfps, 10tw, @30deg [probably tumble]
Sg = 1.16 @ 3500fps, 10tw, under ICAO conditions
(so you can see that velocity is a minor factor)
For my 95VLDs and 26" barrel chambered in 6BR:
Sg = 1.52 @ 2975fps, 8.5tw, under ICAO conditions
Last edited by Mikecr; 08-13-2011 at 12:29 PM.