I admit it I'm confused about twist rates.
Iv'e decided on getting a 6.5x55 but what twist rate is the best to shoot both light and heavy
bullets?
Thanks
David

I built mine on a '98 Mauser action and used a Douglas #1 contour 1-9" twist. Remington uses a 1-8" twist in their .260 and the M'96 Mauser used a 1-7 1/2" twist.
Personally I have no use for the very long 160 grain bullet and I'd use 1-9" again as it's working fine for me.

There's absolutely no reason you wouldn't be happy with a 1-8" twist for all bullets however.

Most of the “cheat-sheets†use bullet weight as the factor in determining twist...while most ballistic experts use the length and shape of the bullet as the factor.

The Greenhill formula has worked for allot of years and it is pretty simple to use. It is based on his “rule†that twist in calibers equals 150 divided by the length of the bullet in calibers.

Use a 175 grain Sierra Match King .308 as an example:

1. Divide the length of the bullet by the caliber in inches: 1.241†length/.308= 4.023

2. Divide 150 (Greenhills constant) by 4.023 = 44.74. This number is the required twist in calibers. to convert that to twist in inches...

3. Multiple 44.74 by .308 (the caliber in inches) to get the twist in inches required to stabilize that particular bullet= 11.5 inches.

This is a “guide†and obviously is open to tweaking to a certain degree in one direction or the other by experimentation with your loads in your barrels. Most .308’s shooting 150 to 180 grain bullets have either a 1-10 or a 1-12 rate of twist, and both have their supporters and detractors.

Wow I'm going to have to print this out and have a
study.
Thanks for all your input its been great I think.
Multiple 44.74,dide 150 by 4.023???
Yes I,m going to sit dowm and have a good think.

David

quote:

Originally posted by Hutzpah:
Wow I'm going to have to print this out and have a
study.
Thanks for all your input its been great I think.
Multiple 44.74,dide 150 by 4.023???
Yes I,m going to sit dowm and have a good think.

David

It sounds far more complicated than it actually is. As long as you know the length of your bullet, and you use a calculator, you can have the answer in less time than it took to read this.

A great book, for those who are interested, is “Understanding Firearm Ballistics...Basic to Advanced Ballistics, Simplified, Illustrated & Explained“...by Robert A. Rinker

Thanks Rick 0311
To be honest I am enjoying learning about rifles amunition and how that work. I have started reloading and just finished making a stock.

David

Mine is like Vapodog's, M98, 1 in 9" Douglas. I use 140s, very accurate.

quote:

Originally posted by Hutzpah:
Thanks Rick 0311
To be honest I am enjoying learning about rifles amunition and how that work. I have started reloading and just finished making a stock.

David

David,

Get the book I mentioned and also get a copy of Hatchers Notebook. Those two books contain more useful info on firearms, ammunition and ballistics than anything else I have ever read.

One of the many interesting jobs General Hatcher had for awhile was getting to see what it would take to blow a rifle up. Now that had to be fun!

There are several good sources of figuring out twist rate for bullets used.

The simplest way is to pick up the phone, call who makes your selected bullet and ask. Did it a few weeks ago with Sierra, told the tech support individual what bullet I wanted to shoot, and he knew what was ideal, and close for the bullet selected. Took about two minutes total for the answer. Dan Lilja has a good listing posted on his web site also. But the bullet manufacturers know what they designed the bullet to work on.

quote:

Originally posted by Hutzpah:
I admit it I'm confused about twist rates.
Iv'e decided on getting a 6.5x55 but what twist rate is the best to shoot both light and heavy
bullets? Thanks David

IF you plan on using the long 160 grainers, your twist rate must be no slower than 1 turn in 8.5"..... This was derived using the Greenhill formula and a Sierra 160-grain bullet, which appears to be slightly longer than the Hornady 160-grainer.

I note the Brownell twist rates are given for bullet weights, and not length. For example, your .30 caliber rifle may shoot 220-grain round-nose bullets acceptably with a twist of 1/10", but it will probably need a quicker twist for the long, pointed boattailed Sierra 220-grain MatchKing.

It is bullet LENGTH, and not weight, which determines how fast they must spin to keep the point out in front.....

El Deguello,

You will find that most barrel makers also use the bullet weight theory for twist...while most, if not all bullet makers use the bullet length theory of the Greenhill formula.

I had a well known barrel maker tell me that a 1-12 inch twist was “very border line“ for 175 grain bullets in .30 caliber. Sierra‘s techs told me just the opposite saying that 1-12 inch is probably the best for that bullet. Of note is the fact that the USMC uses a 1-12 twist on their 308 M40’s firing 175 grain bullets and if that twist did not stabilize the bullet properly they would change to another that would.

quote:

Originally posted by Rick 0311:
El Deguello,

You will find that most barrel makers also use the bullet weight theory for twist...while most, if not all bullet makers use the bullet length theory of the Greenhill formula.

I had a well known barrel maker tell me that a 1-12 inch twist was “very border line“ for 175 grain bullets in .30 caliber. Sierra‘s techs told me just the opposite saying that 1-12 inch is probably the best for that bullet. Of note is the fact that the USMC uses a 1-12 twist on their 308 M40’s firing 175 grain bullets and if that twist did not stabilize the bullet properly they would change to another that would.

Just how LONG are those 175-grain bullets??

The Sierra 175 grain .30 caliber BTHP Match Kings are 1.241 inches in length. I don’t load my own ammunition so I got that measurement from the Sierra tech guys.

quote:

Originally posted by Rick 0311:
The Sierra 175 grain .30 caliber BTHP Match Kings are 1.241 inches in length. I don’t load my own ammunition so I got that measurement from the Sierra tech guys.

So the Greenhill formula says the optimum twist for that bullet would be 1/11.466". I guess then 1/12" would be pretty close!

I remember GEN Hatcher telling of an instance in which a rifling machine at Springfield Armory "slipped a gear", and was turning out barrels rifled 1/11" instead of the standard 1/10" for the '03 Springfields. The way this error was discovered was that a certain number of new rifles were consistently more accurate than the average. So they went seeking the reason for this, and discovered the "slower twist" in the ones that were shooting better, tracing the "problem" to one specific rifling machine. Naturally, the Army repaired the "faulty" machine, so that it was back to making less accurate 1/10" twist barrels. I believe this happened in the days when the Army was using the 172-grain M1 boattail bullet in the '06, but am not sure.

El Deguello,

The conclusions on Greenhill’s formula drawn by Robert Rinker in his book on Ballistics says that the Greenhill formula is pretty much dead-on-the-money for velocities up to a bit over 2,000 fps. Above that speed you should go on the slower side of the figure arrived at in the Greenhill formula to get the best twist to stabilize your bullet.

Factory barrels have to have a “happy-compromise†twist built into them since the factory has no idea what bullet, or velocities will be used in that rifle. Allot of people will buy a new factory rifle and find that it doesn’t shoot accurately with their pet hand load. They start trying to “fix†the problem by doing anything and everything...EXCEPT, trying a different load with a different bullet that more closely matches the twist of the barrel.

To quote Mr. Riker: “Gyroscopic stability varies as the square of the rifling twist. This means that a very slight change in twist will have a disproportionately big result. Changing twist on your rifle? A small change will make a big difference, perhaps more than desired.â€

quote:

I remember GEN Hatcher telling of an instance in which a rifling machine at Springfield Armory "slipped a gear", and was turning out barrels rifled 1/11" instead of the standard 1/10" for the '03 Springfields. The way this error was discovered was that a certain number of new rifles were consistently more accurate than the average. So they went seeking the reason for this, and discovered the "slower twist" in the ones that were shooting better, tracing the "problem" to one specific rifling machine. Naturally, the Army repaired the "faulty" machine, so that it was back to making less accurate 1/10" twist barrels.

If there was an ESOP's Fables of the firearms industry this one makes it with ease. Cute story!!!.......I reaslly don't think there's any beef in this sandwich however.

Hutzpah

I had the same trouble when I ordered my 6,5-06. Dr Geoffrey Kolbe of Border barrels suggested 1-8,5 or 1-8. http://www.border-barrels.com/

I know many 6,5X55 with 1-9 that has problems to stabilise long 140 grain bullets such as Barnes X, Trophy Bonded, Swift or Nosler.

Cheers
/JOHAN

Thanks for the input everyone.
I just looked up Sierra Bullets web site to find out the lenght of there
85grHP
140gr SMP
160gr SBT
No such luck they don't have the bullet lenghts on there site.Schromf was right when he said "pick up the phone".
Hornady was no better as I didn't see any bullet lenghts.
As I have recently finished a custom rifle and as cash is low I was looking at buying a
factory rifle.The confustion strated when I was told by CZ imports that the CZ Lux was 1:12 twist so I looked at a Tikka T3 Hunter and was told that it had a 1:10 twist.
I now have found out that Howa have a 6.5x55 barrel and action (cheap) with a 1:8 twist.
It looks like the 1:8 sounds best(johan,vapodog). I think thats the way to go and I could have anther go at making a stock.
I did'nt want to do be limited in bullet selection as I and this rifle will end up in OZ soon
G-d willing. It would be great to be able to us it from fox and up wards.

Hutzpah (Divid don't forget you are Hutzpah!!)

Hutzpah,

I believe that your large bullet spread is going to make it difficult to get a twist that will properly stabilize all of them...but good luck.

1:8 for mine every time.

quote:

Originally posted by Rick 0311:
Hutzpah,

I believe that your large bullet spread is going to make it difficult to get a twist that will properly stabilize all of them...but good luck.

A 1in8 will stabilise them all and likely give excellent accuracy with 100gr Ballistic tips. My own 6.5 is 1in8 and is most accurate with 100gr BTs despite the fact that the original long CIP throat is now doubly long and the bullets are miles from the lands.

1in8 and forget about it

Oh and many barrel makers only guarentee twist to within 0.5inch. Ordering the 1in8 means you may get a 7.5 or an 8.5 both of which will work fine with the whole range of bullets. Order a 8.5 and you might get a 9 which won't.

I didn't take time to read all the replies, as I'm in a hurry, but you're talking about one of my favorite rounds. Having experimented with this caliber a lot, I offer my opinion. I wouldn't have one that wasn't at least 1-8", or 1-7 1/2", I believe the Remington 1-9" is too slow for the heavier bullets. You should remember that a 140 grain 6.5mm bullet is mighty long for it's caliber, so twist is important. The old Swedes were 1-7 1/2" I believe and they shot up to 160 grainers. The part that's hard to understand is there's no reason to go so slow as 9"?????

If one “standard†twist would properly stabilize all bullets from 85 to 160 grains there wouldn’t be much point in barrel makers offering other twists, now would there? It’s obviously not a marketing scam since the price doesn’t vary with the twist requested...and it is not in the makers best interest to sell something that will not shoot well with the stated load.

The variation in “actual twist†from the top barrel makers is FAR less than one half inch.

Just got in from work then got on the phone to Sierra bullets Technical Service.
The nice guy on the phone said "go for the 1:8 twist that will work on them all".
Then I read your posts and it all seems to tie together.
So 1:8 twist it is. Feeling at peace about it now so hopefully within the next day or two I will order a Barreled Action.
Thank you very very much for spending the time to write.

Hutzpah

It's nice to help the British. Complicated, but nice.

Good luck with your 6.5 x 55. It's a great cartridge.

quote:

Originally posted by DobleTroble:
It's nice to help the British. Complicated, but nice.

Good luck with your 6.5 x 55. It's a great cartridge.

And also quite appropriate since “Greenhill’s Formula was a product of Professor (Sir) Alfred George Greenhill who was not only born and bred in England, he was also Knighted in 1908. For 30 years he was a professor of mathematics to the advanced class of artillery officers at Woolrich Military Academy in England. His formula for determining proper twist was published first in the texts he wrote for the Royal Artillery Institution.