Twist rates and Stabilization

[versifier]

Is there a series of charts that lists rates of twist in different calibers and the bullet weight ranges for optimal stabilization? I know the basic rules-of-thumb, but would like to have some charts to print out and stare at while I'm thinking.

[Jeffreytooker]

Versafier:

Here it is. Put it in an Excel Spreadsheet and it will give you all of your answers. Or you can do it with a calculator.

Jeffrey

GREENHILLS RIFLE TWIST FORMULA

The Greenhill
formula is an empirical equation that does a good job of
establishing twist.

Greenhill's formula is commonly used to determine twist.

Greenhill made easy:

-----------------------------------------------------------------
T=150 x D
---
R

here: T is the twist required,

D is the bullet diameter (in inches)

R is the bullet length to diameter ratio, (length divided by
diameter)

The number 150 is a constant used by Greenhill and works well at
velocities of 1500 fps or greater. At 2800 fps the constant can
be changed to 180 with good results.
rsely, to find out how long a bullet will stabilize in a
given twist use:Subject: L=150 x d x d
-----
T (that is, 150 x D squared divided by T)

Note that it is bullet LENGTH, not weight that is important.

Hope this helps.

[versifier]

Is length the bearing surface of the bullet, or the total length?

[joeb33050]

Is there a series of charts that lists rates of twist in different calibers and the bullet weight ranges for optimal stabilization? I know the basic rules-of-thumb, but would like to have some charts to print out and stare at while I'm thinking.
Go to the CBA site, castbulletassoc.com. FORUM, FILES 2.1.5.1 "The Greenhill Formula" and see the charts you're looking for. You'll have to sign in, as usual, but it's free. Near there are comments by John Ardito on twist, with Forrest Asmus writing as we speak on long range and twist. His work will be there soon.
joe b.

[felix]

Total length. ... felix

[HORNET]

Versifier,
Several options are available. The simplified Greenhill that Jeffreytooker posted works fairly well for most cast boolits. The 150 constant that everyone argues over was derived from the full Greenhill by plugging in typical values for the 220 Gr. roundnose for the .30/40 Krag. The more your bullet, velocity, and atmospheric conditions vary from those used in the simplification, the more inaccuracy there will be in the calculated results.
If your heavily into math, the full Greenhill and a discussion can be found online at http://www.fulton-armory.com/ARTwists .
For simplicity, you can go to http://www.varnintal.com/twist.gif and print off a chart for the simplified Greenhill for several different calibers.
The chart that I usually use was published in the 1962 Gun Digest ( 16th ed.), republished in the 20th ed in 1966, and republished in RIFLE #25 (Jan/Feb 1973) and done by John Maynard ( although Rifle attributed it to Warren Page). This has the advantage of allowing you to check for stability at different velocities, which comes in handy. This works for boolits or the red pretenders if you ignore any plastic tips and use length to the end of the core on match HP's.
Should give you plenty to think about.

[versifier]

Hornet, I can't get either of those links to work. I try them again later and see if I have better luck.

[HORNET]

versifier,
Try http://www.fulton-armoty.com then look for the twist link. The other should be http://www.varmintal.com . Sorry 'bout the typo's, must have a defective keyboard operator or something.

[versifier]

Thank you Hornet, got them both. Looks like I have some reading to do!
Joeb, can't seem to find their site, never visited it before as I've found a good home here. Can you post the link, please?
Felix, any idea why it uses total length instead of bearing surface? It doesn't seem to make as much sense. I must be missing something here.

[felix]

Twist requirements are based upon the external air/moisture friction the boolit sees. Longer the boolit, the more sidways friction. The fatter the boolit's nose, the more frontal friction. A long skinny boolit requires more rotation than a short fat boolit, because of the amount of rotating energy/inertia stored in the boolit should be the same for the same rotational results. ... felix

[Duckiller]

Without a major analysis, you are spinning a top. The bearing surface is what you use to spin the top, i.e.the string. this is why short,fat boolits require a slower twist than long skinny ones to stand up (stabilize). Wonderful things can be dicsovered when playing with toys.

[joeb33050]

Thank you Hornet, got them both. Looks like I have some reading to do!
Joeb, can't seem to find their site, never visited it before as I've found a good home here. Can you post the link, please?
Felix, any idea why it uses total length instead of bearing surface? It doesn't seem to make as much sense. I must be missing something here.

castbulletassoc.org works when I put it in the address place.
Then click FORUM, then click FILES. Somewhere you have to sign on, it's free and easy.
joe b.

[alamogunr]

Precision Shooting had a fairly extensive article on the Greenhill formula in one of the 2005 issues. Mine are stored right now so I don't know which one it is in. It was interesting but gave me more information than I was prepared to use.

John