I've seen .366 barrels in 1/10" twist (typically 9.3X62) and in 1/14" twist (typically 9.3X64). I want to build a 9.3X64 and would like some input on which twist I should select.
Thanks.

99% of European rifles in 9.3x62 and 9.3x64 have 1-14“ twist. My 9.3x62 has 1-14” twist and I have never seen a 9.3mm rifle with other than 1-14 “ twist. Works great with bullets from 220gr. to 325.gr

I know I shouldn't post this, because of all the argument it will cause, but I'm gonna anyway.

The twist has nothing to do with the cartridge case from which the bullet is fired. It is dependent mainly on the length of the bullet itself.

To get the correct twist for your rifle, measure the lengths of the bullets you will want to fire (not the cartridges, but the projecticles).

Then take the length of the longest of those bullets, and plug it into the twist calculator you will find here:

kwk.us/twist.html

Some folks will tell you you can reduce the rate of twist if you increase the velocity enough.

Great theory.

In practical application, though, you CAN'T increase the velocity enough in the vast majority of loads and cartridges to make any useful difference at all.


A very workable rule of thumb is if you are not quite sure which to use, "Twist A" or a slightly slower "Twist B", go with Twist A. A little bit too quick a twist will do no meaningful harm, but a slightly too slow twist will make the bullet unstable in flight, causing innacuracy, reduced range, less penetration in the target, and all kinds of other "bad" things.

I thought my CZ 550 Hog Back is concidered a Euro rifle and it is 1/10" 9.3x62

quote:

Originally posted by Fat_Albert:
I thought my CZ 550 Hog Back is concidered a Euro rifle and it is 1/10" 9.3x62

CZ does some strange things ... here is the description for the 550 Medium Lux:
"The Lux style stock feels like an extension of your arm when coupled with iron sights. The adjustable “U” small notch sights on this rifle are optimized for precision shooting at longer range."

Sounds good right? But the 550 Medium Lux is only available in 7MM Remington Magnum which is an atypical iron sight calibre.

The Ruger M77 African in 9.63x62 is 1/10" as well.

AC, I've already run some of the optimal twist calculations and came up with 1/14" to 1/17" for the heavier 9.3 bullets I want to shoot. I'm curious because of the faster twist 9.3 barrels out there. I have a 1 in 14" Lothar Walther barrel and I think I'll use it.

Thanks.

A 1 in 14" twist will stabilise all weight projectiles.

quote:

Originally posted by Code4:
A 1 in 14" twist will stabilise all weight projectiles.

That seems clear enough. Why would major manufacturers go with the faster twist?

quote:

Originally posted by ForrestB:
AC, I've already run some of the optimal twist calculations and came up with 1/14" to 1/17" for the heavier 9.3 bullets I want to shoot. I'm curious because of the faster twist 9.3 barrels out there. I have a 1 in 14" Lothar Walther barrel and I think I'll use it.

Thanks.

Sounds good to me, Forrest. I didn't even know there were 1-in-10 twist 9.3 barrels, but then I never looked to see, either. So now you guys have tweaked my interest, and I'm gonna have to measure the twists in my 3 different makes of 9.3s and see what they are....

Let us know how it works out, please. I have one of the original charter-offer MRC stainless magnum short actions that I originally bought two of. One to build a 9.3 WSM on, and the other for a .416 WSM well before anyone else had done either.

Unfortunately, a stroke intervened and the 9.3 WSM of mine has never gotten done. But I still hope to do it...still have the action.

And a buddy used the other identical action for the .416 WSM and it is great. Perks right along.

The CIP spec for both the 9.3x62 and 9.3x64 mandate a max of 1:360mm or 1:14 twist and thus one would find that any production gun built in a CIP signatory country would have this twist.

Mauser's original barrel spec for the 9.3 x 62 was 1:360 so was Brno with their ZG 47 first built in 1950. Brno used the 1:360 barrel for both the 9.3x62 and 9.3x64.

I have a Original Otto Bock 9.3x62 and that too has a 1:360 twist barrel

Forrest
You might want to pick a bullet you want to shoot first. If you're using the larger TSX, they need a little more twist than the jacketed of similar weight.

My 9,3x64 has a 24 inch 1:14 barrel. Shoots pretty well with everything from 220 to 320 grainers..

M

quote:

Originally posted by gunmaker:
Forrest
You might want to pick a bullet you want to shoot first. If you're using the larger TSX, they need a little more twist than the jacketed of similar weight.

Second what James said. Determine the longest bullet you will likely use and then pick the twist rate that will stabilize that bullet.

My 9.3x62 has a Shilen barrel with a 1:12 twist.

quote:

Originally posted by ALF:
The CIP spec for both the 9.3x62 and 9.3x64 mandate a max of 1:360mm or 1:14 twist and thus one would find that any production gun built in a CIP signatory country would have this twist.

Mauser's original barrel spec for the 9.3 x 62 was 1:360 so was Brno with their ZG 47 first built in 1950. Brno used the 1:360 barrel for both the 9.3x62 and 9.3x64.

I have a Original Otto Bock 9.3x62 and that too has a 1:360 twist barrel

That's very interesting, as Fat albert posted this:

quote:

Originally posted by Fat_Albert:
I thought my CZ 550 Hog Back is concidered a Euro rifle and it is 1/10" 9.3x62

So, Alf, are you telling us that CZs are not made in a European country signatory to CIP standards?

Or is it possible that CIP is one recognized standard, but not one used by all makers in all signatory countries?

Or what?

quote:

Originally posted by Alberta Canuck:

quote:

Originally posted by ALF:
The CIP spec for both the 9.3x62 and 9.3x64 mandate a max of 1:360mm or 1:14 twist and thus one would find that any production gun built in a CIP signatory country would have this twist.

Mauser's original barrel spec for the 9.3 x 62 was 1:360 so was Brno with their ZG 47 first built in 1950. Brno used the 1:360 barrel for both the 9.3x62 and 9.3x64.

I have a Original Otto Bock 9.3x62 and that too has a 1:360 twist barrel

That's very interesting, as Fat albert posted this:

quote:

Originally posted by Fat_Albert:
I thought my CZ 550 Hog Back is concidered a Euro rifle and it is 1/10" 9.3x62

So, Alf, are you telling us that CZs are not made in a European country signatory to CIP standards?

Or is it possible that CIP is one recognized standard, but not one used by all makers in all signatory countries?

Or what?

I agree with you AC. It's better to err on the faster side then the slower. There's an awful myth for years that too fast a twist utterly destroys your accuracy and it does not. In the case of the 9.3 we speak of here it sure as hell isn't a target rifle or caliber in my opinion.

AC:


CZ USA 550 FS actually has a twist of 1:9.5 inches

What I can state though is that if the same gun was produced in factory as a production gun in a Country that is a CIP signatory then that gun has to comply to the CIP rules.... it is not a choice it is a matter of law.

The CZ guns that are made in the Czech Republic as well as their barrel blanks have a 1:360mm twist as shown on their website and this complies with the CIP ruling

Many of the the Current CZ USA hunting rifles have barrels made and fitted in the USA and are not available from CZ elsewhere in the world.

Well, that makes sense Alf (once we have the part about the rifles being barreled here). But, without the explanation it sure didn't.

For whatever reason(s), at least four barrel makers here seem to offer 1-in-12" twists (Lilja, Krieger, Shilen and PacNor). I don't know about Shilen & Kreiger, but 12" twist is the ONLY twist PacNor and Lilja offer for 9.3 barrels.

I would guess it is because of the increasing use of monometal bullets here, which are long for a given weight, and the fact that heavier and heavier bullets are gaining popularity amongst those from here who go to Africa or Alaska and want a rifle which will deal with whatever gets up in front of them, if need be. At any rate, I have never heard any complaint about any 9.3 barrel from any of those four makers.

I have read reports of Lothar Walther (also located in the U.S.) making both 12" and 14" twists in 9.3, but have not been able to verify that at their website.

If I was going to buy another 9.3 barrel right now, I'd get either a Lilja or a PacNor, in 12" twist. I do not believe the slightly quicker twist would hurt any, and there might come to be instances when it would help.

Twist/bullet length is a factor when shooting at extreme distances. This is not something one will do with a 9.3x62. If you are building a rifle, go with the tightest twist you can get. A 9.5" twist is an excellent idea for a 9.3x62. Someone was thinking with his mind and not his heart when that happened.

Forrest,

I have two 9.3x64 Brenneke's.

23" Lother Walther 1:14
23" Half Moon 1:12

Neither like the 250gr TSX.
Both shoot the factory RWS 293gr TUG into an inch.

quote:

Originally posted by SDhunter:
Forrest,

I have two 9.4x76 Brenneke's.

Damn, I have to get me one. That's 12mm longer and .1mm larger than my 9,34!

Just so folks are clear on the subject of my posts when I refer to using "Less" twist, by less twist I mean a slower twist...1-in-14" for instance being "less" or "slower" than 1-in-12"...i.e., it does not turn the bullet as fast as the 1-in-12", it turns it slower.

I personally would not choose a 1-in-9.5" super fast twist barrel if I have a choice, but I WOULD choose something faster than the old classic 1-in-14" twist if I could...especially if I wanted to (or had to in California) shoot the newer, longer, monometal bullets. And I CAN use something faster than the 1-in-14" twist. There are at least four makers of 1-in-12 twist 9.3 barrels in the U.S., probably more.

Too fast a twist doesn't make any major difference with high quality bullets. It MAY make a difference with mediocre quality ones. Just like one can spin a top too fast for it to fully stabilize the instant it leaves the string, you can do the same thing with a bullet, if the bullet isn't perfectly balanced and doesn't have its center of form concentric with its center of gravity.

If the bullets are not well balanced and really, truly, round they will travel a bit longer distance outside the bore before they settle down to a steady spin. That can affect short range accuracy in the distance covered before they settle down to spin evenly...again, just like a top. An imperfectly balanced top ( poorly made one) will not settle down as quickly as a perfectly balanced one will.

It WILL NOT affect accuracy enough to miss an animal, or to miss a vital spot on an animal either, but it MAY cause the bullet to be more prone to tumble when it strikes the animal, thus somewhat reducing penetration...especially if the bullet happens to be very long and very pointed.

Too slow a twist also fails us, as it not only doesn't stabilize the bullet initially, the problem only gets worse as the bullet slows down on its trip to the animal.

So, I always encourage folks to get neither extreme...not too fast, and not too slow, for any diameter of bore and lengths of bullets.

As there are many makes of bullets out there of good form and roundness, speaking only for myself again I prefer a marginally faster twist than what may be the calculated optimum, rather than a twist which is marginally too slow.

As a result, in the 9.3 I would prefer a 1-in-12" twist over either a 1-14" or 1-9.5" twist.

(If I made my own barrels so that I could have whatever I want, I'd go with 1 turn in 11").

Thanks Mike,
Didn't do a very good job proof reading did I?

quote:

the problem only gets worse as the bullet slows down on its trip to the animal.

Why do you say that?

AC:

Regarding to fast a twist: The contention is that one can overstabilize the projectile ?

Common wisdom would have it that overstabilization is a non issue in flatfire trajectories ? Well that at least holds true for cannons and large bore military guns.

Yet those who shoot long distances choose just enough amount of twist for the to give stability once it egresses from the barrel. ie a stabilization factor of around 1.3 at muzzle and no more? A big SF at bore means a bigger SF downrange and a bigger SF means a smaller tractibility number (whether this is important to the 9.3 per se I do not think because the 9.3 x62 is hardly a long distance caliber )


But there is another reason and I believe it to be valid.

What is the twist angle of a .366 cal bullet at 1:9 inches ?

A 1:10 .366 bore barrel is cut at a twist angle of 6.6 degrees and that is at the absolute limit considered as the cut off where bullets slip in bore. If you make it tigher than 7 deg the bullet slips and that not only cuts down on accuracy it causes excess wear in the throat both due to mechanical and blow by mechanisms.

Hi Alf, I was under the impression that all else being equal you can get more velocity from a barrel with a slower twist than a fast one.

As it relates to target shooters the 155gr bullet is mandated by certain competition classes and the BC of those being about as high as practicably achievable, the faster they're pushed the better. I have been led to believe that the standard 1-10" is excessive for this weight of bullet and something like a 1-13 or 1-14" will give a small velocity boost over another rifle of nominally identical specification but a faster twist.

Have I got this completely wrong or is there some truth to it?

quote:

Originally posted by Gerard:

quote:

the problem only gets worse as the bullet slows down on its trip to the animal.

Why do you say that?

Because the rotation slows down and does not speed up. It slows very little and at a very slow rate of reduction, so the problem does not worsen rapidly, but it does worsen. If the bullet could travel far enough (which it can't) it would eventually stop turning at all.

quote:

Originally posted by ALF:
AC:

Regarding to fast a twist: The contention is that one can overstabilize the projectile ?

Alf, it is not MY contention that one can overstabilize a bullet. To me that is an oxymoron. How can something meant to fly be too stable in flight?

I do think that one can overspin a bullet IF it is not made sufficiently well to "balance" as it enters the medium (air) at that rate of spin.


Alf's post, continued...

"Common wisdom would have it that overstabilization is a non issue in flatfire trajectories ? Well that at least holds true for cannons and large bore military guns.

"Yet those who shoot long distances choose just enough amount of twist for the to give stability once it egresses from the barrel. ie a stabilization factor of around 1.3 at muzzle and no more? A big SF at bore means a bigger SF downrange and a bigger SF means a smaller tractibility number (whether this is important to the 9.3 per se I do not think because the 9.3 x62 is hardly a long distance caliber )


"But there is another reason and I believe it to be valid.

"What is the twist angle of a .366 cal bullet at 1:9 inches ?

"A 1:10 .366 bore barrel is cut at a twist angle of 6.6 degrees and that is at the absolute limit considered as the cut off where bullets slip in bore. If you make it tigher than 7 deg the bullet slips and that not only cuts down on accuracy it causes excess wear in the throat both due to mechanical and blow by mechanisms.

That sounds reasonable to me.

But I also suspect the spin rate at which slippage MUST occur because of the physical properties of the bullets and bores differs between monometal bullets and traditional jacketed bullets,. I do not know if that is correct, but from what I have seen of both, I suspect it is. That may act to ameliorate some of the problems inherent in cup'n core bullets in moderately faster twists.


And to a similar extent that 9.3 bullets are not normally (yet, anyway) used as target shooting bullets, likewise thay are not fired in the numbers that target bullets are. So, for my use anyway, I am not greatly worried about tearing the throats out of my barrels faster than I can afford to rethroat or to rebarrel if needed.

I still think a slightly more rapid twist than 1-in-14" would not be a bad thing considering the trends in modern bullets, but I also do not believe in going to any opposite extreme unless it is required. Moderation in all things seems to me to apply just about as well to shooting as to anything else.

Anyway I am not interested right now in participating in a prolonged discussion of ballistic theory on the subject. I find my existing 9.3 barrels (3 European, 1 American) all shoot well with the traditional bullets I like best (286 grain Normas). But I have recently bought a lot more monometal ones of longer lengths which I have not had the opportunity to use in several different barrels. If I was going to buy yet another barrel, I would get a 1-in-12 twist for any additional rotation that might prove to be needed in actual practice.

As a former Palma Team member, I AM aware of what it takes to do the job in some smaller bores at out to at least 1,000 yards (I also used to shoot a fair bit at up to 1,200 yards with both a .308 and a .300 Magnum, and out to 1,600 yards with a larger .300 Magnum.)

quote:

Originally posted by SDhunter:
Thanks Mike,
Didn't do a very good job proof reading did I?

You mean that was just a typo? Drat, here I was looking forward to building myself a new rifle!

Alf,

quote:

A 1:10 .366 bore barrel is cut at a twist angle of 6.6 degrees and that is at the absolute limit considered as the cut off where bullets slip in bore.

We have been involved in much work with 1:8" twist .375" calibers, at launch speeds much higher and with heavier bullets than any 9.3 caliber. Accuracy from 100m to 1600m is excellent. The spin up torque that would induce slippage is certainly much higher with these calibers than what it would be with a 9.3. The only time I have seen slippage has been with calibers that have unusually long freebore dimensions. Freebore length is a far bigger factor that promotes slippage than the rate of twist. Longer freebore lengths also allows more gas to bleed past the bullet and thereby increase throat erosion. The culprit is not tighter twist, it is freebore length.

AC,

quote:

Because the rotation slows down and does not speed up.

The rotational velocity does slow down as the bullet goes downrange. The forward speed slows down much faster than rotation. Stability is the result of the ratio of forward speed and rotational speed. This means that stability increases as the bullet goes downrange, it cannot decrease. See 'Static Stability' at this page where the quote below is sourced:

"Obviously, the static stability factor continuously increases at least for the major part of the trajectory or more generally, always exceeds its value at the muzzle. Generally, it can be assumed that if a bullet is statically stable at the muzzle, it will be statically stable for the rest of its flight."

Ah static stability: is "more stability" better and how much "more is better" ?

And no slippage at high twist rates...... if I recall Will called someone on pics of GSC bullets posted right here on AR clearly showing signs of slippage.

For flat fire conditions:

Static stability increases as distance increases. Penetration increases as distance increases. As stability factor increases, terminal performance increases (if the bullet design is sound). What is not to like?

For extreme range conditions:

Static stability increases as distance increases. If static stability becomes too high, the bullet fails to nose over the trajectory. Tractability is reduced. So, stability factor that is too high is only a factor for extreme range applications.

Yes, I posted the picture of slippage and those were the bullets fired from rifles with long freebore lengths, not from tight twist rates. This one was from a 460 Weatherby.



The text that accompanies this picture from Feb 2010 is:

quote:

The anomaly on the drive bands is interesting. We only see this with calibers or rifles that have a long freebore and shallow lead angles. The bullet travels through the freebore and gathers enough speed, due to the length of the freebore, that the shallow leade angle does not cause it to start rotating immediately when it finds the rifling. In this case the bullet took almost the entire shaft length to balance the spin up torque against the resistance from the drive bands on the bullet. The same bullet fired in a 450 Rigby or 458 Win Mag shows normal engraving with no skidding at the front.

The specified twist of a 458WM is tighter than the specified twist of a 460 Weatherby while a 450 Rigby is slower.

Here's a list of some bullet lengths for the 9.3mm,
The calculated barrel twist needed using the Greenhill formula and
The corresponding rifling angle:

Prvi-P 285 RN-SP, 1.24", 1:16.2", 4.1°

Swift 300 "A", 1.32", 1:15.2", 4.3°

Woodleigh 320 RN-SP, 1.32", 1:15.2", 4.3°

Nosler 286 PT, 1.38", 1:14.6", 4.5°

Barns 286 Solid, 1.38", 1:14.8", 4.5°

Nosler 250 AB, 1.4", 1:14.4", 4.6°

Barns 286 Triple-S, 1.58", 1:12.7", 5.2°

Ray,
So many people depend on Greenhill for reliable results and do not realise the flaws of the system. They act in good faith because it is held up as the model.

The twist number for both Barnes bullets are wrong. Greenhill works only with flat base, tangent ogive, lead core bullets. Even the Nosler numbers are somewhat off.

It is frustrating to see it being perpetuated by so many sources where the unsuspecting relies on getting a good result.

Greenhill was first used in the late 1800s and it is time to discard it because simplistic solutions have been made redundant by much better methods.

http://www.border-barrels.com/barrel_twist.htm

I think 1 n 12" twist is great for the medium bores, .358 to .375. Why did they ever use 1 n 16" for the original 35 whelen?

quote:

Originally posted by Gerard:
Ray,
.....

It is frustrating to see it being perpetuated by so many sources where the unsuspecting relies on getting a good result.

.....

Don't be fruatrated - Works fairly well in this 9.3x62 case.

quote:

Originally posted by Gerard:
AC,

quote:

Because the rotation slows down and does not speed up.

The rotational velocity does slow down as the bullet goes downrange. The forward speed slows down much faster than rotation. Stability is the result of the ratio of forward speed and rotational speed. This means that stability increases as the bullet goes downrange, it cannot decrease. See 'Static Stability' at this page where the quote below is sourced:

"Obviously, the static stability factor continuously increases at least for the major part of the trajectory or more generally, always exceeds its value at the muzzle. Generally, it can be assumed that if a bullet is statically stable at the muzzle, it will be statically stable for the rest of its flight."

I have heard that argument for many years...usually stated as "Since the forward velocity slows quicker than the rotational velocity, obviously the bullet turns more rpm for every foot of travel as distances increase."

True enough for the most part, but that presumes that a slower spin is still adequate to stabilize the bullet in flight at a slower speed. That presumption, based on my own long range shooting experiences, I do NOT buy holus bolus.

Recall, please that the Greenhill formula realates to the length of the bullet as one of the major factors in the calculation. Bullets of such and such a length require so and so spin rate. And, bullet length does NOT normally change in flight, regardless what occurs with spin and forward velocities.

I know that is a gross oversimplification, but it is something worth keeping in mind when discussing THEORIES of bullet flight.

I believe there may be a threshold spin rate which must be maintained or exceeded to assure flight stability regardless of the forward rate at which the rifle bullet is traveling.

I also believe maintaining that spin rate is possibly even more important as the bullet may start to encounter the different flight problems met as its velocity drops through the sonic barrier, where stability is more difficult to maintain.

So, basically my own actual shooting experience suggests to me that we need to start with a quick enough spin that, even as the bullet rotation decreases, it remains above a particular "calculateable" floor rate of spin for its whole flight to the distance(s) we want to use it.

Greener's formula may be overly simple for some projectile mass/form/velocity combos, but don't throw the baby out with the bath water.

quote:

I have heard that argument for many years...usually stated as "Since the forward velocity slows quicker than the rotational velocity, obviously the bullet turns more rpm for every foot of travel as distances increase."

It is not an argument or a debatable matter, it is fact, proven many times over. If a bullet is statically stable at the muzzle, it is statically stable for the rest of the trajectory.

Static stability is dependent on launch speed, bullet length and shape and the flow field over the bullet. Only the launch speed is a simplistic element. The bullet shape and flow field are made up from many variable elements and all are important.

Example:

Under ideal atmospheric conditions and with a 1:10" twist, the approximate stability factor of a given 168gr 30 caliber bullet at the muzzle is
3000fps = 1.15
2000fps = 1.06
1200fps = 0.82

Therefore, when launched at 1200fps and checked at 25, 50 and 100m, it is tumbling end over end.
The same bullet, when launched at 3000fps, goes through the transonic to subsonic (1200fps to 1000fps) with some yawing but no tumbling. It has a higher stability factor, downrange at 1200fps, than when launched at 1200fps.

This is why one cannot predict how a bullet will deal with an impact medium at 300m, by loading it down to simulate the 300m impact speed at a shorter distance, while using the same rifle.

Greenhill depends mostly on length because it assumes a tangent ogive, flat base, lead core for the rest. It has become useless with the advent of secant and hybrid ogives, boattails, hollow points, partition, solid shank, solid nose and monometallic bullets.

Useful links for barrel twist:

http://www.border-barrels.com/barrel_twist.htm

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

http://kwk.us/twist.html Read the entire page on this one, please.

It is impossible for a bullet to lose static stability downrange, and to stop spinning before forward velocity has stopped.

quote:

Originally posted by Gerard:
.....

Greenhill depends mostly on length because it assumes a tangent ogive, flat base, lead core for the rest. It has become useless with the advent of secant and hybrid ogives, boattails, hollow points, partition, solid shank, solid nose and monometallic bullets.

.....

Gerard,

Come back down to earth and get back on this thread regarding the 9.3x62 barrel twist!

I'm not picking at you. I posted that info above to help so we could have some FACTS to discuss rather than just opinions and theories.

I'm most interested in Nolser 286 PT, the Swift 300 "A", and the Barns 286 Solid. AND am willing to listen.

Show us how the Greenhill formula would compare to the links you posted. Some examples on how one or the other would lead to a better decision on picking a barrel twist for the 9.3x62.