"Puting it to sleep too early" & "Overstabalization"

[Mikecr]

[ QUOTE ]
Over spinning (spinning faster than necessary) amplifies the effects of any mass imbalances.
This will cause a loss of accuracy. Will you notice it going from one twist number to the next? Probably not.
Benchrest guys are pretty particular about what twist they want though.

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Point blank BR shooters use flat based bullets with low IY/IX ratios. This is why they can get away with lower stability, and reap the benefits of reduced twist.
Longe range bullets require more stability for good performance. So if I were you, I would go conservative.

Put another way: You would likely be hard pressed to even proove increased dispursion due to overspin(unless bullet integrity comes into play). But you will very easily identify the dispersion associated with too slow of twist for a bullet. It turns on like a big ol switch!

[RBrowning]

My understanding of "over stabilization" isn't a concern because of bullet failure, though that surely happens too, but it is a concern at the later stages of a bullet's flight.

Assuming that you are firing on the level, your bore will be canted up ever so slightly. This sends your bullet upward to counter the effects of gravity. At some point your bullet reaches it's highest point and begins to come back down in a near parabolic arc, the farther it goes, the steeper it's drop angle.

Normally the nose of the bullet should be in line with the path of the bullet. This reduces the drag on the bullet. This is pretty much a given early in the bullet's flight. Over stabilization comes in when a bullet is spinning too fast, making too good of a gyro and resists the tendency of the body to follow inline with the path of the bullet. This gives a nose high attitude and increases drag. If your bullet is just stable the drag on the body will tend to keep it behind the nose and on line of the bullet path. That keeps your BC high, drag low, and makes happy shooters.

But then again, this IS rocket science, and I didn’t even stay at Holiday Inn Express last night!
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[threeinadime]

Thanks for all the insightful replys. I had know idea it was this interesting a question. Has anyone worked out a formula for barrell twist that would tell you that if you wanted to shoot a .30 caliber, 165 grain bullet, the ideal twist rate is (for example) 10.756 ? Is it this exact or is there still alot of voodoo in this. For example, I want to build a Tactical 20 (.223 necked to .20 caliber and shoot 32 thru 40 grain bullets) and everyone (almost) can shoot great groups with a .204 Ruger (almost the same cartridge)with a 1 in 12 twist, but most can not get the 40 grain pill to group like the 32. So, knowing this, do I ask for a 1 in 11 or 1 in 11.5? Is there a way to calculate best fit and best overall compromise fit?

[meichele]

[ QUOTE ]
Normally the nose of the bullet should be in line with the path of the bullet. This reduces the drag on the bullet. This is pretty much a given early in the bullet's flight. Over stabilization comes in when a bullet is spinning too fast, making too good of a gyro and resists the tendency of the body to follow inline with the path of the bullet. This gives a nose high attitude and increases drag. If your bullet is just stable the drag on the body will tend to keep it behind the nose and on line of the bullet path. That keeps your BC high, drag low, and makes happy shooters.
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That is a fact!! [img]/ubbthreads/images/graemlins/smile.gif[/img] I have been crittizized in the past for preaching just that but I choose to stick by that and keep my twists as slow as I can for the longest bullet I will be using.

[1doug]

try www.riflebarrels.com (lilja barrels)it has the twist chart that is user friendly