Twist rates for elr?

[NEMTHunter]

Keep in mind that SG and dynamic stability compete. Once the bullet goes 30° off the firing line, dynamic stability trumps SG. This is particularly critical once you go transonic with long bullets. The pressure leverage will flip and tumble the bullet. Gyroscopic stability is like salt in your food, too much makes it too hard to correct.

Could you explain please? The faster the bullet spins the less trouble it has going from super sonic to subsonic. IE through the trans sonic range.

 

[jasent]

That's the opposite of my experience.

 

[NEMTHunter]

@NEMTHunter
A very high, or even a comparatively high SG will keep the bullet pointing in the direction of the line of fire but when the bullet begins dropping, an angle divergence occurs and the bullet starts tilting belly forward. In this state, wind effect gets exaggerated and penetration suffers. When approaching transonic, this long bullet starts tumbling. A more moderate spin allows the bullet to enter the transonic state less abruptly because the center of pressure has less torque to overcome. Chey-Tac figured this out for us years ago and that's why their system can do what others can't. If your terminal velocity is likely be above 1250ft/s, spin away to your hearts content but if it's likely to be less, I wouldn't recommend a high SG.

Thats interesting. The reason I asked was From what I have heard and see A under spun bullet will tumble long before a "over" spun bullet will. At least that been my understanding. From what the ELR guys have said. Its better to have more twist then right on the edge. Specifically when going through the tran-sonic range.

I can easy test the over spun farther since my "big" 30 cal is a 7.5 and The 230's are 3300 plus fps at muzzle.

Interesting topic for sure. Would like tho see how that plays out. The thing with the chey-tac are there system is not the one winning the ELR matches.

Thanks for answering. Keep the Data coming.

 

[Deleted member 71114]

As far as the ELR matches and whats winning, trends and why. The 416s have become popular only because of seeing trace better with the larger bullets, seeing splash better in the dirt, rocks and sand at the 2000 plus yard range over the 375s

I will be pushing a 505 grain 416 in the 3250 fps range out of a 39" 8 twist this year we will see what happens. Last year I was pushing a 400 grain 375 at 3361 fps out of a 35" 8 twist as well.

Osoh

 

[slv hunter]

Good stuff. So what's the " perfect" SG.

 

[Deleted member 71114]

When it comes to long solids and ELR I still refer back to the 20 cal per turn formula and this will get you to a optimum choice.
20 x .375 = 7.5 twist. As stated we ran 8 twist
20 x .416 = 8.32 twist and yes I will be pushing the envelope at again a 8 twist on the 416

Cheers
Osoh

 

[jasent]

I wonder why my long heavy for caliber vld style bullets that are "over" stabilized transition so well?

 

[jasent]

Yes bullets hit nose first past transonic, past subsonic with repeatable results.

 

[jasent]

"

Most rifle bullets eventually achieve hyper-stable flight if they fly far enough. Gyroscopic stability Sg increases throughout the flight. By achieving it right out of the muzzle, however, the rifleman is minimizing yaw-drag on his bullets during the critical first several coning cycles of flight where the bullet's coning "angle-of-attack" is usually largest and where the "potential drag force" (q*S) is always its very highest."

Jim Boatright

 

[jasent]

I'm getting my mv with magneto speed. Using applied ballistics for calculating dope drops and down range speed
These are actual results not just predictions.

 

[jasent]

Your welcome to come shoot it. Would be fun to setup a high speed camera at the target.
G7 bc is .351
Berger elite hunters @3025fps
2200ft asl
Temps from 20°F to 75°F has been conditions ive shot at these distances with this rifle.
You can not have repeatable results with tumbling bullets.

It used to be a fact the bullets didn't transition well. "Transonic Barrier"
Then it was a fact that vlds didn't transition
Now it is a fact that people are transitioning vlds/uld through transonic flight with higher than traditional sg.

 

[RockyMtnMT]

When it comes to long solids and ELR I still refer back to the 20 cal per turn formula and this will get you to a optimum choice.
20 x .375 = 7.5 twist. As stated we ran 8 twist
20 x .416 = 8.32 twist and yes I will be pushing the envelope at again a 8 twist on the 416

Cheers
Osoh

Question for you. Do you have any thoughts on the Miller stability formula and different material density?

 

[NEMTHunter]

There is a difference between using a chy-tac based round and using chy-tacs system.

@jasent
Thanks, I'll also need the temperature and barometric pressure of the shot along with the bullet B.C., if the G1 B.C. of that bullet exceeds .617, that bullet is keyholing or tumbling outright 95% of the time and I'll wager $1,000 to witness that proved wrong in person.

It will tumble most of the time. In fact it will all the time. IF you have to slow of a twist. OR a poor bullet design.

I do not bet. But your bet is a sure loss. Why? The guy you are saying its not possible to has been doing the very thing for a bit. Thats like telling somebody you cant melt lead on a stove top, when in fact you can.


My question to you is this. Have you personally tested the theory out. Or just going from reading? The reason I ask is there has been supporting data and you say it not possible for it to work. Where is Your supporting data?

I ask not because I am trying to call you out. But to see how and why it did not work for YOU.

Again some bullets Regardless of twist will NOT transition well. Others do it like its nothing. Its my belief that the long Solids need MORE twist then a cup and core bullet does per the same length going through the transition. This is a opinion formed only from research on what has worked and what has not worked.


My question to you is this. Will a Berger 215 Hybrid shot @ 3400 FPS in a 7.5 twist with a G1 BC of .354. Shot @ 2000 feet above sea level in 50% humidity @ +70F shooting south transition and hit point first after dropping down to subsonic. Bullet length is 1.598
How about the same conditions just the bullet speed is 3300 FPS and the weight is 230 grains and length is 1.608

 

[HARPERC]

.......When it comes to long solids and ELR I still refer back to the 20 cal per turn formula and this will get you to a optimum.......

We have a 1-6" twist .264 in early stages. This formula would suggest a 1-5.28".
.308 becomes 1-6.16".

Any examples of these being in use?

A 1-8" .375 doesn't sound over the top, but the 5-6" twist seem to always draw criticism valid or otherwise.