What in your opinion should be the rate of twist for a new 9.3X62. I would like to shoot the heavy bullets, 300 gr and 320's. Thanks maddog

Can somebody help me here?

Maddog,

This may not help much but my CZ550 in 9.3x62 has a 1 in 9.5" twist - based on CZ literature. No problem with bullets up thu 286 grain including a fairly long 250 grain Barnes X. I remember reading that twist rate was related as much to the length of the bullet as well as the weight.

Might be worth a call to someone like Charlie Sisk who worked on some 9.3 wildcats or some of the barrel manufacturers with 9.3mm experience.

Phil

IIRC, my CZ 550 in 9.3x62 has a twist rate of 1-14".

Twist rate needed as calculated by the Greenhill formula:

150 X D^2/L = Twist

Where:
D = bullet diameter in inches
L= bullet length in inches
150 = a constant

I'm not an expert on twist rates. I have read where the Greenhill formula is considered to be conservative (ie: it estimates a faster twist than may be needed). Here's some info I found on twist rates: http://www.loadammo.com/Topics/July01.htm

-Bob F.

Check the various barrel maker's websites. They have reference pages for caliber/twist/weight of bullet. You can always give them a call too-that's what they are there for.

http://www.lothar-walther.de/html/161.php
This page shows a 1-280mm twist in 9.3x62, or ~ 1-11" twist. I guess Lothar Walther is a good place to drop an eamil and ask them your question.

http://www.lothar-walther.de/html/159.php
This website lists the 9.3 diameter as a 1-360mm twist. At 25.4 mm/inch, that's 1-14" twist. It didn't say what recommended bullet weights it will handle

Very helpful. Thanks guys...Maddog

[QUOTE]Originally posted by Phil:
Maddog,

"This may not help much but my CZ550 in 9.3x62 has a 1 in 9.5" twist - based on CZ literature." Sirs, this is my first post. I've been lurking for some time as I am the "new" owner of a CZ550 in 9.3x62. When this subject of twist was brought up before, I went and tested my rifle and came up with 1 in "about" 14 inch twist, using the old range rod and tape measure. My 55 shoots the Norma 232 Vulkans better than any other bullet leading me to believe that the 1 in 14 is correct. Has anyone else CONFIRMED that their rifle has a 1 in 9.5 twist??? Shrps74

I looked up the twist rate info in CZ's 2006 catalog. It does indeed state that their 9.3x62 rifles use a 1-9.5" twist. However, I think that is a mistake or misprint. Like shrps74, I tested my rifle and came up with about 1-14" using the cleaning rod method like he did. Of course, CZ could have changed the twist rate since I bought my rifle but 1-9.5" is just an awfully fast rate of twist for a .366 caliber.

Just trying to be helpful....

-Bob F.

IIRC, the 9.3x62 made its name with a 14" twist. All mine are custom barrel jobs, and I used a 12" twist. Never had any problems with any bullet I've tried through the 300 Swift, which is probably more difficult to stabilize that the 320 RN bullets...

Also, the 375 H&H uses 12" twist as the standard, which can handle up the 350 Woodleighs...

I've "heard" that CZ switched their twist rate from 14" to 9.5" at some point, though this is mostly hearsay...

IIRC - I too own a CZ550 American in a 9.3X62. I measured mine after Bob F. indicated his was a 1:14 twist; mine is also 1:14. I called CZ in Kansas City to see if they produced the faster twist; the rep. (claimed to be a gunsmith) there said it was actually 1:10. He also said they make their own barrels. They either have a different method of determining twist than the rest of us or the guy is actually a sales rep. passing himself off as an "authority". Anyway, mine shoots 250gr through 286gr bullets under an inch at 100 yards any "day-of-the week" if I do my part. Regards, Mags

Maddog
I use a 1 x 12 twist on all the 9.3 rifles I build, that stabilizes everything up to the 320 grainers. I've never shot anything heavier. I use that twist on everything from the 9.3 BS to the 9.3 Sisk # 4 which is a 378 Wby necked to 9.3. Hope this helps.
Charlie

I will check the twist rate on my CZ550 (circa 2002) when I get home later this week. I assumed the twist rate info from CZ was correct. You know what they say about assuming!!

Will update this thread with an actual measurement.

Phil

Gentlemen I must say I find this fascinating, especially the formula ( Greenhill method ) that BFaucett posted.
Does anyone else have another formula for calculating the twist, it would be interesting to run some comparisons as the Greenhill method was noted as being conservative.
In real life there may not be a hill of beans difference from a 1:12 to a 1:10 or 1:14 twist but it is always good to be armed with as much info as possible to make the best decision.
Sorry I hope this isn't a hijacking!

My PAC-NOR is a 1 - 12", 9.3 X 62 but, I haven't fired it yet. Don't know what the accuracy will be.

quote:

Originally posted by Masterifleman:
My PAC-NOR is a 1 - 12", 9.3 X 62 but, I haven't fired it yet. Don't know what the accuracy will be.

Two (soon to be three) of my 9.3x62s have pac-nor barrels. One SS and two CM. All have a 12" twist. The two already built are extremely accurate - could not be more pleased. All on model 70 actions. BTW, I think the #3 pac-nor contour is perfect for a 9.3x62 (the #4 is a bit stout)...

Here is a target from a zeroing session for my SS barreled 9.3x62 - #4 pac-nor. (Shot last spring/summer.) A 3-shot group, a 5-shot groups, and then a final 2 shots that got me just where I wanted to be...

What is the best barrel length guys?? 22, 24, 26
Your thoughts?? Maddog

Mine's 24" FWIW.

CIP (European equivalent of SAAMI) has standard twist at 1-14". Designed to stabilise standard 286gr bullets.

Mine own is an LW 14 twist that shoots 232gr into ragged holes and 286gr partitions into an inch.

I have a 1 in 12 twist with 23" length on my gun. It loves 286 grain bullets. I have not tried anything heavier. It also shoots the factory Lapua 270 grain bullets in one hole.

quote:

Originally posted by MADDOG:
What is the best barrel length guys?? 22, 24, 26
Your thoughts?? Maddog

I like the 22.5-24" range. My next one is going to have a 59cm barrel - roughly 23.25"....

quote:

Mine's 24" FWIW.

and has a 12 twist for the 320 Woodleighs should I ever feel the need!

Alfred Greenhill came up with his formula for figuring twist rates in artillery barrels toward the end of the 1800's. The constant is variously given as 150 or 180.

I use 180 FWIW.

I measured my CZ 550 FS at 1:14" twist. This is a rifle I ordered in 2004 and I had to wait 3 months for delivery. It must have come straight from the factory. I certainly is not 1:10", so the CZ-USA catalog must be wrong. The instruction manual is from the factory and does not list the twist rate.

It shoots OK, typicaly 1.5-2.5" at 100 yds. I am happy with it for what I bought it for.

(Hi Phil . . Measure your's yet?)

Well, add my CZ to the 1:14" twist group - based on an actual measurement this time!! This rifle was purchased new in 2002.

The heaviest bullet I've shot is 286 grains but it handles it very well with very good accuracy typical for the CZ550. Barrel length is close to 24 inches which seems to be plenty. A bit shorter barrel might be handy at times though.

Phil

My 9.3x62 has a 24" Douglas barrel with a 12" twist. It shoots the 286gr Barnes X well often making one hole three shot groups at 100yds.

One of these days i'll get some heavier bullets just to see how they do.