Miller Twist Formula

[Fearnowind]

Been working with the Miller Twist Formula and I keep running across a constant of "720" for the calculations (720*Velocity/Twist=RPM)
I must be missing something because I can't for the life of me figure out what that constant is based upon. Anybody got a hint? :-X

 

[Fearnowind]

Thanks. That'll make a nice spread sheet calc.
When I read the article at http://bulletin.accurateshooter.com/2008/06/calculating-bullet-rpm-spin-rates-and-stability/
it speaks about Miller's formula and includes the data "Bullet RPM = MV X 720/Twist Rate (in inches)" and that's driving me nuts.

 

[Steve Blair]

Thanks. That'll make a nice spread sheet calc.
When I read the article at http://bulletin.accurateshooter.com/2008/06/calculating-bullet-rpm-spin-rates-and-stability/
it speaks about Miller's formula and includes the data "Bullet RPM = MV X 720/Twist Rate (in inches)" and that's driving me nuts.

[br]
Additional to Donovan's comments:
It is because the velocity is expressed in feet per second, twist in inches and RPM is revolutions per minute. You must reach common terms between these three expressions and that is inches per second, so 12 * 60 = 720 (inches per foot * seconds per minute).

 

[jscandale]

Never heard of the Miller formula. Sounds to me like some guy named Miller had a big ego for such a simple calculation. Here's how simple:

12" (1 ft)
----------- X muzzle velocity (fps) X 60 seconds = rotational vel (RPM)
barrel twist

Example: 8" twist bbl @ 3000 FPS

(12"/8") x 3000 fps x 60 sec = 270,000 rpm

JS

 

[GSPV]

Miller's Formula is to describe gyroscopic stability factor or, equivalently, the twist required for stability.

http://en.wikipedia.org/wiki/Miller_twist_rule

 

[jscandale]

Miller's Formula is to describe gyroscopic stability factor or, equivalently, the twist required for stability.

http://en.wikipedia.org/wiki/Miller_twist_rule

Ah..that's much different.

JS

 

[bricktop]

Here is a quick internet calculator for the lazy (like myself).

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

 

[mshelton]

I saw the title and was expecting to see something on the twist of the miller lite beer bottle neck and it's stabilizing ability on the horse pi$$ contained within.