Question on Twist Rate

[cwhitt02]

This does make sense to me. It seems there would be something of an optimal spin to stabilize a given bullet, not heavy and light, but I don't know a lot about that.

I know some firearms instructors who were shooting an M-4 with a 1:7. They were trying different grains and found that if they went too light, the round would basically disintegrate in flight.

 

[Corax]

"...around 400,000rpm was where things started getting iffy..."

For 3,000 ft/second and and an 8" twist, it looks like the rotation speed is 270,000 rpm. So 400,000 rpm is pretty hot.

 

[ImBillT]

We appearantly have differing definitions of "blowing up"!

To me there is a major difference between blowing up, and core jacket separation. Especially if the core is still in the jacket.

Well...I’m talking about the core and jacket separating in mid-air. How is that not a blowup? Whatever we want to call it, and we may have been talking about two different things, it is possible to shoot a VLD-H in a manner that causes it to fail to travel 1000yds in a single piece. The cause is that once the core melts, the jacket comes apart mid-flight. This occurred around the same time they started recommending VLDs for hunting. The fix was a thicker jacket, but the thicker jacket tended to act more like an FMJ when hitting gelatin. That’s what resulted in having two lines of bullets.

 

[ImBillT]

"...around 400,000rpm was where things started getting iffy..."

For 3,000 ft/second and and an 8" twist, it looks like the rotation speed is 270,000 rpm. So 400,000 rpm is pretty hot.

I meant to say 300,000. Big difference. Still hard to get there in an 8-twist(3333fps), but easily attainable in a 7-twist(2917fps)

 

[Millsworks]

I think you would be hard pressed to over spin a bullet to the point it won't stabilize.
A loss of speed is the only affects I have personally experienced, from faster twist barrels, and only in the .223 cartridge.
You would have to go very light with a bullet and have an unusually fast for cartridge custom barrel.

 

[std7mag]

Well...I’m talking about the core and jacket separating in mid-air. How is that not a blowup? Whatever we want to call it, and we may have been talking about two different things, it is possible to shoot a VLD-H in a manner that causes it to fail to travel 1000yds in a single piece. The cause is that once the core melts, the jacket comes apart mid-flight. This occurred around the same time they started recommending VLDs for hunting. The fix was a thicker jacket, but the thicker jacket tended to act more like an FMJ when hitting gelatin. That’s what resulted in having two lines of bullets.

There in lies the rub.
The bullet was hitting the target as a single projectile. The core was melting just at the surface contacting the jacket. Allowing the core to shift/spin within the jacket.
Had the core melted to the point where it shed it's jacket (2 pieces) it most likely wouldn't have reached the target at all.
They were experiencing 9-7 ring instead of "X" ring.

 

[ImBillT]

There in lies the rub.
The bullet was hitting the target as a single projectile. The core was melting just at the surface contacting the jacket. Allowing the core to shift/spin within the jacket.
Had the core melted to the point where it shed it's jacket (2 pieces) it most likely wouldn't have reached the target at all.
They were experiencing 9-7 ring instead of "X" ring.

My understanding is that there were guys failing to have the bullets reach the target. Usually toward the end of a long shot string.

 

[std7mag]

No, it never got to that point that i'm aware of.
Mostly fliers in the 9-7 ring off vertically as well as horizontally.

 

[ImBillT]

No, it never got to that point that i'm aware of.
Mostly fliers in the 9-7 ring off vertically as well as horizontally.

Nope. During a test performed by Berger themselves, using 6.5-284s and 140gr VLDs with the original J4 jackets and the new thicker J4 jackets, they documented a number bullets which “failed to reach the berm”. Out of 950 shots, 510 used the original jacket thickness, and 440 used a new thicker jacket. 52 failed to reach the berm. All 52 were bullets made with the original jacket thickness. This led to the VLD-THICK. I had forgotten about that. It didn’t last long before that was renamed VLD Target, and VLDs using the original jacket thickness became called Match VLD Hunting.

Link provided if you’d like to read it.

Berger bullet failure test

First I want to thank Mid Tompkins for doing so much to make this test possible. Without him it would not have happened. Also I want to thank Sherri Hurd and Michelle Gallagher for their part in putting 950 shots down range using a 6.5X284 in a little over 6 hours. You both earned those sore...

benchrest.com

 

[mtmuley]

My dad can beat up your dad. mtmuley

 

[ImBillT]

My dad can beat up your dad. mtmuley

Lols.

 

[tzone]

My dad can beat up your dad. mtmuley

Not if he's twisted too fast