Need help, formula for rifling twist.
01-20-2004, 08:14 PM
#1
Typical Buck
Thread Starter
Join Date: Feb 2003
Location: Eagles Landing, KS
Posts: 612
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.
Thanx for any and all help.
01-20-2004, 08:37 PM
#4
Join Date: Apr 2003
Location: Northern MN
Posts: 270
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
Hope that's what you ment
01-20-2004, 10:21 PM
#6
Nontypical Buck
Join Date: Feb 2003
Location: Crescent Valley, NV
Posts: 2,271
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.
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.
01-21-2004, 05:40 AM
#7
Giant Nontypical
Join Date: Feb 2003
Location: Texas - BUT NOW in Madison County, NY
Posts: 6,270
RE: Need help, formula for rifling twist.
ORIGINAL: charlie brown
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.
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.
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!
