I'm getting ready to have a Mauser actioned .25-06 rebored to 9.3x62mm and had pretty much settled on a 1-12 twist. Just finished reading a two part article at Real Guns about a CZ 550 FS(which is one fine looking rifle!!)chambered in 9.3x62mm. Twist rate? 1-9.5!! I've been researching references on an average twist rate for this cartridge and I had been seeing anything from 1-10 to as high as 1-16. Now 1-9.5 shows up. Some were custom rifles but most were production rifles. Done been the Greenhill route. What's really astonishing is that everyones gun seems to shoot the complete spectrum of 9.3 bullets well,at least that's what their saying. Is this cartridge that forgiving?

til later

Lots of options here. I looked up the Steyr twist for the 9.x62mm, and they use a 14.25" twist. In my own custom 9.3x62mm the barrel is a 22" Pac-Nor, and I have no idea the twist, except that the rifle shoots well with any bullet I feed it.

LLS

EP,
Get a barrel twist fast enough to stabilise the longest projectile available ... Woodleigh's 320gr PP is 1.441" long. Its a big game rifle not a varminter, so must be able to use all projectiles available to it.
Cheers...
Con

what con said...
greenhill formula and then go 1 twist faster .. that is to say, if the formula says 1:28, and the barrel maker has a 1:22 twist, great... use that

CZ may advertize 1:9.5" twist, but they are producing 9.3x62 barrels with 1:14" twist lately.

Check it yourself. Anyone can tell the difference between those two twist rates by eyeball!
(Or use a tight patched jag and a ball bearing handled cleaning rod and a sharpie marker and a measuring tape.)

CIP spec is 1:14".

I would go with 1:12", but would be thrilled by a 1:9.5" twist.
You have made a good choice.

Boom Stick,I hope you had a small box of popcorn cause this shows over!!

Greenhill:
320 Woodleigh= 1-13.9
270 Speer= 1-16.9(I'm starting out with these)
I'm going with a 1-12. Fini!

RIP,ain't doubting you one bit. I didn't get the CZ info from an ad,I got it from a web article where a CZ in 9.3x62 was being tested. He wrote that it had a 20.5"bbl,9.5"twist. Of course I don't know where he got his stats from,but I know where you got yours!

Anyways THANK YALL for the help!! Shows over Boom Stick! LOL

til later

Ballistic theory here can get heated

But I guess the twist wars have cooled and the dead horse has been burried.

I Inquired at Swift regarding the heavy 358 and they said 1 in 12 was his choice. That was my thinking too.

As we have heard the 1 in 16 twist and the heavy bullets in the 35 whelen have an issue.

I think the .008 diff wont make too much diff in the whelen fix theory.

I just like heavy for cal bullets in theory...heavy weight over magnum velocity.

Good luck!

quote:

Originally posted by EP:
I'm getting ready to have a Mauser actioned .25-06 rebored to 9.3x62mm and had pretty much settled on a 1-12 twist. Just finished reading a two part article at Real Guns about a CZ 550 FS(which is one fine looking rifle!!)chambered in 9.3x62mm. Twist rate? 1-9.5!! I've been researching references on an average twist rate for this cartridge and I had been seeing anything from 1-10 to as high as 1-16. Now 1-9.5 shows up. Some were custom rifles but most were production rifles. Done been the Greenhill route. What's really astonishing is that everyones gun seems to shoot the complete spectrum of 9.3 bullets well,at least that's what their saying. Is this cartridge that forgiving?

til later

Seems to me that in Europe, they often make a twist rate in a given caliber a lot tighter than we do for the same bore size- for example, 1/8" for a 7x57mm in their rifles vs 1/9" to 1/10" over here.....

OK,I got to thinking(smell the rubber burning?)how tight is too tight. Using El Deguello's 7x57 as an example,what rate of twist would be too tight and what would happen?

til later

What happens depends on how well the bullet is balanced, any voids, especially near the jacket (outer edge of the bullet) will cause the bullet to fly in a slightly corkscrew path as the extra mass on one side pulls the bullet off line. With a well balanced bullet, all that will be noticed is a slightly less muzzle velocity - but this is more theoretical as it is usually less than the difference of one barrel to another.
With a very high velocity small bore like a 22-250 or 220 Swift, too much twist can cause the bullets to come apart in flight, but you won't see this with a 7x57 or 9.3x62. Maybe with the 408 Chey-tac or 338 Lapua, but doubtful even for them. You need a lot of velocity (~4000 fps) and an extremely high twist rate like the 1 in 8" for shooting those extra long 77 & 80 grain .224" bullets; and then shoot the small and week 40 to 50 grain varmint bullets instead.