Rate of Twist

[Davey Boy]

I read about barrel rate of twist on here a lot.
And am curious about what makes one better than another for certain bullets loaded.

Also where does one find the rate of twist for a particular gun that is about 45 years old. Is it stamped on the barrel somewhere?

Gun is CIL 950C late 60's manufacture, .308 similar to Savage 110C of that era.

[dgitz]

http://www.youtube.com/watch?v=cdoCNZBlRGQ

Here's a good video on measuring rate of twist.

As for which rates are best for which bullets I'll let the members with far more experience than me chime in for that.

[plmnnkoqaz]

Twist rate is how many inches it takes the rifling to make one revolution of the barrel. Eg 1 in 8 twist means that every 8 inches of barrel length the bullet will be spun one time. Optimal rate of twist is going to be different for each cartridge / bullet weight combination. It has to do with a lot of factors, but most simply it comes down to velocity and bullet weight. Heavier, longer bullets need more twist to be stabilized. However if you take two bullets of equal caliber and weight and shoot them at markedly different velocities the optimal twist rate will be different.

It is pretty easy to measure the twist of your barrel.

1) using a cleaning rod figure out the rifles length of your barrel. You can insert the rod from the muzzle and using a light, push it only as far as the rifling, not lathe way in the chamber. Mark this length on your rod with a piece of tape, then measure the rod.
2) Using a proper cleaning rod that is free to rotate, screw in a tight fitting jag and patch and push it from the breach so that it just touches the rifling. Mark the cleaning rod with a piece of tape with an indexing mark on it. Push the rod through the barrel, coining the number of rotations, it can be tricky to get the last fraction of a rotation accurately, but do your best to estimate it.
3) Divide the length of the barrel in inches by the number of rotations and that number (x) will be the 1 in x barrel twist you are looking for.

[Davey Boy]

Ok that looks easy will have to try that.

Thanks fellas.

[Dick284]

Here is a good write up on the importance of the right rate of twist:
http://www.shootingtimes.com/2011/01...trates_200809/

[Leeper]

The rate of twist requirement for a given projectile length is something which was pretty well figured out about 150 years ago but it gets re-hashed every now and then anyway.
The thing is this; it is necessary to have sufficient twist to stabilize the longest bullet you are going to be shooting and having a faster twist than is absolutely necessary does no harm in the real world of hunting rifles and within practical game ranges.
In a thirty caliber barrel, a twist rate of one in twelve inches will stabilize virtually any bullet one is likely to shoot up to and including a 200 grain boat tail. For bullets longer than this, a one in ten will suffice. With lighter bullets, it would take a very accurate rifle and shooter to tell any difference between the two.
On the other hand, if the twist is too slow, there is no chance that accuracy will be acceptable and the bullets will, in fact, tumble.
When choosing a twist rate for a hunting rifle, one can obsess over it or one can simply use a twist which is certain to be acceptably quick for the longest bullet which is likely to be used.
If one is building a target rifle with the intention of using a particular bullet, the choice of a twist which is perfectly matched to that bullet may or may not pay dividends. Again, in general, the important thing is be sure and have sufficient twist.
Twist rates for factory rifles have been established within parameters which suit the cartridge and it's intended purpose. So it is that the 22-250 gets a fourteen inch twist to stabilize the 50 to 55 grain bullets which have been traditionally used in it to fulfill it's purpose as a high velocity varmint round. The 223 was originally designed arouns a 55 grain fmj boat tailed bullet and required a 12 inch twist to stabilize this bullet (barely). Later changes made to extend the range of the 223 by using longer, heavier bullets, led to the adoption of faster twist rates (1 in 9, 1 in 8, or even 1 in 7.5).
The important thing to remember is that a faster twist does not preclude the use of lighter bullets nor does it necessarily mean heavier bullets will be most accurate in a particular rifle. A 308 with a 12 inch twist will shoot any bullet weight up to and including the 220 round nose and just because the twist is slower, it doesn't mean it will be most accurate with shorter bullets nor, if it was a ten twist, would it necessarily be more accurate with longer bullets. As long as the twist rate is sufficient to stabilize a given bullet, there are other factors which will have a far greater effect on accuracy. Leeper.

[ptlfmx]

http://www.gunsandammo.com/2013/12/2...st-rates-ammo/

[DaleJ]

Originally Posted by Dick284

Here is a good write up on the importance of the right rate of twist:
http://www.shootingtimes.com/2011/01...trates_200809/

Nice little article but its wrong. Apparently a 1:12 308 chambered barrel will not shoot a 205 gr bullet. Should I stop shooting mine or just plow forward blindly with the program?

[Pathfinder76]

Originally Posted by Leeper

The rate of twist requirement for a given projectile length is something which was pretty well figured out about 150 years ago but it gets re-hashed every now and then anyway.
The thing is this; it is necessary to have sufficient twist to stabilize the longest bullet you are going to be shooting and having a faster twist than is absolutely necessary does no harm in the real world of hunting rifles and within practical game ranges.
In a thirty caliber barrel, a twist rate of one in twelve inches will stabilize virtually any bullet one is likely to shoot up to and including a 200 grain boat tail. For bullets longer than this, a one in ten will suffice. With lighter bullets, it would take a very accurate rifle and shooter to tell any difference between the two.
On the other hand, if the twist is too slow, there is no chance that accuracy will be acceptable and the bullets will, in fact, tumble.
When choosing a twist rate for a hunting rifle, one can obsess over it or one can simply use a twist which is certain to be acceptably quick for the longest bullet which is likely to be used.
If one is building a target rifle with the intention of using a particular bullet, the choice of a twist which is perfectly matched to that bullet may or may not pay dividends. Again, in general, the important thing is be sure and have sufficient twist.
Twist rates for factory rifles have been established within parameters which suit the cartridge and it's intended purpose. So it is that the 22-250 gets a fourteen inch twist to stabilize the 50 to 55 grain bullets which have been traditionally used in it to fulfill it's purpose as a high velocity varmint round. The 223 was originally designed arouns a 55 grain fmj boat tailed bullet and required a 12 inch twist to stabilize this bullet (barely). Later changes made to extend the range of the 223 by using longer, heavier bullets, led to the adoption of faster twist rates (1 in 9, 1 in 8, or even 1 in 7.5).
The important thing to remember is that a faster twist does not preclude the use of lighter bullets nor does it necessarily mean heavier bullets will be most accurate in a particular rifle. A 308 with a 12 inch twist will shoot any bullet weight up to and including the 220 round nose and just because the twist is slower, it doesn't mean it will be most accurate with shorter bullets nor, if it was a ten twist, would it necessarily be more accurate with longer bullets. As long as the twist rate is sufficient to stabilize a given bullet, there are other factors which will have a far greater effect on accuracy. Leeper.

At the risk of offending someone, great synopsis as usual!

[Pathfinder76]

Originally Posted by DaleJ

Nice little article but its wrong. Apparently a 1:12 308 chambered barrel will not shoot a 205 gr bullet. Should I stop shooting mine or just plow forward blindly with the program?

This is what I love about this stuff. You can take someones word for something he has likely regurgitating (no offence to the deceased), or listen to someone that has actually tried it and reporting same.