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Twist
Jun 11, 2021 5:07:14 GMT -5
Post by fatfred on Jun 11, 2021 5:07:14 GMT -5
I have a basic question: If a bullet is launched from a barrel with a 1:9 twist, at what rate does the twist rate decline as the bullet slows down? So at 500 yds, is it still turning at 1:9? Is there a way to calculate any twist loss and if so, is it a factor in accuracy at long range?
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Twist
Jun 11, 2021 11:56:14 GMT -5
via mobile
Post by joelmoney on Jun 11, 2021 11:56:14 GMT -5
Oops after re-reading your post you are talking spin drift. Yes there are ballistic calculators that will give calculations for spin drift.
I researched this quite a bit the only individual I could find who had researched this in terms of terminal bullet performance Wes Dr Ed Ashby in some work he did for Barnes. He believed rotational velocity does not slow at any practical range. I felt he ment rotational velocity differences couldn’t be measured from 0-600 yards. He was shooting zebra with a 22 hornet and having some pretty extraordinary results. He was working on 7mm and 30 cal bullets when South Africa kicked out all Americans. It is very interesting to see the wound channel of a Barnes X in a 1-7” twist.
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Twist
Jun 11, 2021 15:36:45 GMT -5
Post by fatfred on Jun 11, 2021 15:36:45 GMT -5
I'm not sure we are talking the same thing, but maybe we are. When you take a top or a jack and spin it on a table, it eventually slows down, wobbles and falls over because it's losing the stabilization of the spin. I just wondered if bullets slowly loose their rate of spin as they travel down range. I can't imagine that they don't lose something over distance. I think of silly examples like firing a bullet straight up in the air. Eventually it come to a dead stop. Is it still spinning? As it returns to earth, falling back down, is it still spinning? These questions have no particular reason to be asked, I was just being curious.
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Twist
Jun 11, 2021 15:44:41 GMT -5
via mobile
Post by joelmoney on Jun 11, 2021 15:44:41 GMT -5
The way I understood what I listened to on his podcast as that the bullet rotational velocity never really gets shed. A top slows due to the friction of the point on the surface that it spins. My only experience that makes me believe this is if you spin magnetized bearings the seem to spin forever when suspended. I will try finding the podcast it was very interesting.
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Twist
Jun 11, 2021 17:20:48 GMT -5
via mobile
Post by joelmoney on Jun 11, 2021 17:20:48 GMT -5
Starts about 15 min mark currently listing I’ll try getting the time for your answer but think you will find some very good information if you start listening there. About 18:20 I believe starts answering your question if I am understanding you correctly
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Twist
Jun 12, 2021 6:05:56 GMT -5
Post by fatfred on Jun 12, 2021 6:05:56 GMT -5
Interesting guy. It sounds like if the spin does slow down at all, it's not enough to worry about. It also seems that a screaming 120 TTSX out of my 7mm Mag going 3425 fps may actually kill better at 500 yds than 100 yds. And the 250 Mono we shoot in the SOCOM is sort of hitting "nice and slow" to get the benefits of 90 degree petal deployment. I like listening to guys like that. Thanks for the link.
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Twist
Jun 12, 2021 12:29:10 GMT -5
via mobile
Post by joelmoney on Jun 12, 2021 12:29:10 GMT -5
I find his archery studies very informative. Would enjoy picking his brain sometime.
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Twist
Jun 12, 2021 17:17:05 GMT -5
via mobile
Post by joelmoney on Jun 12, 2021 17:17:05 GMT -5
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Twist
Jun 13, 2021 12:25:55 GMT -5
Post by fatfred on Jun 13, 2021 12:25:55 GMT -5
That's quite a video. When you figure that a bullet, even a slow pistol bullet has RPM's approaching 100,000, you can imagine how fast that thing was spinning on the ice. Even after running into a "brick wall" of ice...that didn't even stop the spin. I guess when you look at the 100's of gel test out there, you can see a spiral effect in them when the gel is of the clear type.
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Post by bkm on Jun 16, 2021 5:14:10 GMT -5
Two things are required for a bullet to remain stable in flight. Twist Or gyroscopic spin and velocity. As u know we choose our twist rate for the bbl based on the bullet’s length, diameter and velocity. When the bullet exits the bbl it’s forward momentum and spin (rpm) is the fastest it will ever be however the velocity will diminish much quicker than the rpm’s causing the bullet to eventually tumble. Actually the bullet is harder to stabilize at the muzzle when it’s velocity is the highest. As it slows in velocity the rpm’s aren’t diminishing as fast thus the bullet becomes more stable. This has been referred to as the bullet going to sleep. I hope this helps. I also think about things like this myself. . I’m not smart enough to know the answers. I’m just passing on things I’ve read about. Brian Litz offers a few good books pertaining to this.
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