Need help, formula for rifling twist.
 

Can anyone give me the formula for figuring rifling twist. I have miss-placed my notes and going from memory I get answers that I know can't be right.
Thanx for any and all help.

RE: Need help, formula for rifling twist.
 

What do you mean by that?

How to figure it for a particular barrel?
For a certain caliber?
For a certain weight bullet?

Not quite following you.

RE: Need help, formula for rifling twist.
 

Do a search on "greenhill formula".

RE: Need help, formula for rifling twist.
 

Draw a line on your cleaning rod, rod must have a free spinning handle. Place in barrel with a tight fitting jag and patch so the rod will turn with the rifling. Place a mark on the rod at the barrel and feed the rod in until the line rotates to the starting point, mark again. Pull out the rod and measure. Twist rate is 1 in X where X= measurement b/t the marks.

Hope that's what you ment;)

RE: Need help, formula for rifling twist.
 

Greenhill formula!!!!!!!
I had forgotten the name.
Thank you,I'll see if I can find it.

RE: Need help, formula for rifling twist.
 

How's this?

for a .30 cal. 180 gr. Spitzer bullet that is 1.35 inches long. here is the formula.
150 divided by length of bullet in calibers. Only applies to bullet with specific gravity of 10.9- jacketed rifle bullets.

1.35/.30= 4.5 calibers; 150/4.5= 33.33 calibers, or that many times the diameter of the bullet. 33.33 x .30= 9.9999 or 1 in 10" twist.

This came from Mastering Mule Deer by Wayne Van Zwoll, and was referred to as the Greenhill formula.

RE: Need help, formula for rifling twist.
 

This is the Greenhill Formula, (developed by an instructor at the British Royal Artillery School in the late 1800's) as described in Hatcher's Notebook:

Twist (in calibers) = 150/length of bullet in calibers.

It works for ALL regular jacketed bullets. But, as the example given by Charlie Brown shows, the answer will come out approximate, eg., you use a 1/10 twist for a bullet that requires a twist of 1 turn in 9.999 inches, etc. Naturally, a twist that will stabilize a bullet of a given length will also stabilize all bullets of that same caliber which ARE SHORTER!! Weight of the bullet does not enter into this formula, ONLY LENGTH of the bullet matters!

RE: Need help, formula for rifling twist.
 

Thanks to all of you for your help, I now have what I need.

Thanks again