Twist Rate For Long Range Target

[mike1340]

Looking for advice or personal experience on witch rate of twist would be better for long range target shooting.
I'm interested in 6.5×284 Norma Savage F class rifle with 1-12 or Savage bench rest with 1-8 rate of twist. Interested in 1000yd target acquisition. I do know a little about spin drift but not enough to make a decision. Thanks mike1340

 

[Klint Beastwood]

You'll probably miss more by trying to over compensate or having a bad day shooting in general then worrying about spin drift at that distance depending on the size of your target. I'm only at 2/10's of a mil at 1050 for spin alone...so what...about 7 something inches? with a 6.5 creed.
Normally when talking about twist rate, one would be asking what would best stabilize a particular weight projectile out of a particular cartridge.

 

[mike1340]

Yes, of course . So the faster spin will be better suited for the heavier projectiles

 

[Klint Beastwood]

yes sir.

 

[taliv]

start by picking a bullet. then pick a suitable rifle

 

[mike1340]

Yes sir, I get very good results with the 140 grain ELD out of my Savage 12 LRP so with that said I'm going with the Savage BR 6.5 × 284 Norma.

 

[mike1340]

I get good results with the 140 grain ELD -X out of my Savage 12 LRP 6.5CREED.
Most likely going with the Savage BR 6.5 × 284 Norma 1-8 twist.

 

[ATLDave]

Note that Brian Litz (ballistics engineer for Berger Bullets and a long-range competitive shooter) has come out with some research suggesting that the benefits of increased twist do not stop at the same "is it stabilized yes/no" binary point that most have assumed. I'm not remotely knowledgeable enough to opine on such matters, but, IIRC, he claims his data show that, at long ranges, "super-stabilized" bullets (i.e., those rotating significantly faster than required to prevent oblong impacts) will shoot more precisely than those that are rotating slower, but still fast enough to punch round holes.

He's got a couple of books. You may want to give them a read.

 

[jmr40]

Try this

http://www.bergerbullets.com/twist-rate-calculator/

 

[old heeler]

Might get on this site forum as they still have F-Class shooter post about 6.5x284 Norma

http://www.accurateshooter.com/cartridge-guides/65x284/

 

[mike1340]

Thanks for all your help, I'm checking out the different websites and it is big help /lots of good information

 

[hdwhit]

ATLDave wrote:
...the benefits of increased twist do not stop at the same "is it stabilized yes/no" binary point...

I agree. But, if this leads to the conclusion that ever faster twist rates are endlessly beneficial, it becomes fallacy. The limiting factor, is what angular forces the projectile can tolerate before breaking apart. Increase the twist rate and the angular forces on the projectile increase.

I can, for example, shoot Hornady 50 grain SX bullets all day long at around 2,900 fps from my Ruger Mini-14 with a 1:12 barrel and make nice round holes in the target.. If I try to shoot those same loads out of my S&W M&P-15 with a 1:9 barrel, I get what looks like a puff of gray smoke about halfway to the target and no holes in the target.

 

[Archie]

Generally speaking, a faster twist is required for longer bullets in a given caliber. However, consider 'proper twist' is more likely a 'range' than a single answer.

One can 'over spin' a bullet, but a lot of 'over spin' is preferable to just a little 'under spin'. Also consider some enterprising soul or company will someday make a 160 grain (or 10.1 gram, the European and 'old' standard for 6.5mm caliber) and the barrels made for 140 grain bullets may not work properly.

HDWhit makes a good argument in the other direction ("...endlessly beneficial..."). The late P. O. Ackley once made a barrel for (as I've read it) a .219 Donaldson Wasp with a 1:5 twist (seeing if twist had any effect on pressure). The .22 bullets used would act as HD relates. Spun themselves to death, so to speak.