Twist rates for elr?

[RockyMtnMT]

Question to you guys that are working in the 2 mile world. What is the general consensus on twist rates? Are you needing higher sg to be consistent or marginal sg?

My world of long range ends at about the 1500y mark and I prefer to have high sg for good terminal performance for hunting. This subject came up on another thread and I have been under the impression that elr target crowd is working with higher or over stabilized bullets for good performance through the transonic. Let me know if I need to be corrected.

Thanks for your input.

 

[HARPERC]

Tagging in!

 

[jasent]

I'm running sg of 2.7 and staying stable through transonic. My next barrel I'm trying sg of 3.0

 

[Brett Bracken]

I have stupid question....what is sg??

 

[jasent]

Sg is bullet stability factor.
http://bergerbullets.com/twist-rate-calculator/

I have stupid question....what is sg??

 

[Brett Bracken]

Thank you sir

 

[Deleted member 71114]

Here's a little explanation on the theories of Sg

Gyroscopic Stability
Various estimators for calculating the required rifling twist-rates for adequate gyroscopic stability Sg for rifle bullets have been used since the Greenhill Formula of the mid-1800's. We also now use Don Miller's formulation for VLD-type bullets and Bob McCoy's McGYRO calculations developed for artillery projectiles. A common feature of these estimators is that they all rely heavily upon the bullet length L in calibers as a type of slenderness ratio of the projectile. Some formulations also adjust for muzzle velocity, air density, and the average material density of the projectile.
Ideas are changing about what values of Sg constitute adequate and desired initial gyroscopic stability, especially in the flat-firing of rifles to extended ranges. Formerly, we considered an initial Sg of 1.2 to 1.4 to be adequate for best short-range rifle accuracy. Now, we realize the advantages of reduced aerodynamic drag if we provide our conventional jacketed, lead-cored rifle bullets with an initial Sg of at least 1.5, as recommended by Bob McCoy and Bryan Litz. Riflemen are now learning to launch the new monolithic copper-alloy ultra-low-drag (ULD) bullets with an initial Sg of 2.5 to 3.0 for best results in extreme long-range (ELR) shooting. This requires a rifling twist-rate of about 20 calibers per turn for monolithic ULD bullets of about 5.5 calibers in length L. The resulting bullet spin-rates at high muzzle speeds are not compatible with use of conventional jacketed lead-cored match bullets.


Cheers
osoh
JH

 

[jasent]

I'm shooting lead core jacket bullets ( Berger elite hunters) with sg of 2.41 with zero issues out to 1800 yards. Today's bullets can be spun much faster than 1.7

I've also shot sst's With sg of 3.15 out to half mile. No issues and bc stays true.

 

[HARPERC]

......I'm running sg of 2.7 and staying stable through transonic. My next barrel I'm trying sg of 3.0.......

Which combination of twist and bullet will this be?

I'm having trouble visualizing-In my mind I see long, heavy for caliber bullets, being the mainstay for ELR, and at the same time, especially with the mono's getting twist's fast enough (1.5) in general can be an issue.

Example Steve has put together a 165ish, 6.5. No barrel maker really jumped with enthusiasm to provide a 1-6" twist. If I remember correctly about 1.8 is where SG ends up.

 

[jasent]

I'm shooting a 1:9 twist 338 shooting mostly 250gr bergers (just double checked sg 2.41 not 2.7)but also some 225gr sst's with sg 3.15.

My next barrel will be 1:6.5 .338 or 1:7 .375 but will mostly shoot monos

K&p will make just about any twist rate you want

 

[dfanonymous]

https://www.ballisticmag.com/2017/12/22/long-range-master-2-mile-shot/

I believe that you need to speed up your twist off standard twist a little bit. I think if you use certain software that you can run some simulations and test different twist/bullet lengths both on paper or simulation, then in the field for stability.
So I'd look at the ammo one plans on using first and get confident with that first, then find what's best able to stabilize it at extreme ranges.

Look at randy Powell's mentioning around the 50 cal. Military standard twist for a similar gun would be a 1:15.

 

[dfanonymous]

 

[jasent]

This was written for monos but I have found it has worked well with jacketed bullets ime with the bullets I've used


Hopefully this link is allowed
https://forum.snipershide.com/attachments/hyper-stabilized-rifle-bullets-pdf.6876555/

 

[Techy]

Tagging in.

Building on an 8 twist and trying your 227's and 214's for what it's worth. Will have more to share later