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Forum Index > Precision long range hunting and shooting > Fascinating stuff - Projectile behaviour

Fascinating stuff - Projectile behaviour

07 Apr 2020
@ 07:44 pm (GMT)

Apriori

Hi All,
I have often read extreme accuracy benchrest stuff where they talk about the projectile "going to sleep", and have always thought; "Pull the other one".

I reckon this clip from "The Slow Mo Guys" demonstrates exactly what they mean - but using a shell instead of a bullet.

The projectile actually oscillates, up-and-down, side-to-side, along it's long axis until it stabilises properly. I reckon THAT's what they mean by "goes-to-sleep" - it stabilises along the long axis.

https://youtu.be/z0SVHm6-KUQ?t=517 (watch until approx the 09:30 mark)

It also might partly explain why a shot at the muzzle is so utterly devastating - the projectile is moving at it's maximum speed, and has maximum possible energy, but is also really unstable. It looks like it would not take much at all to make it tumble.

Again, there are a LOT of assumptions here, ie mainly that a bullet will behave like a scaled down artillery shell, but I think this illustrates the "going to sleep" concept almost perfectly.

Science is so interesting !

Replies

1
07 Apr 2020
@ 11:19 pm (GMT)

Jesse Sully

Re: Fascinating stuff - Projectile behaviour
Beautiful stuff. thanks
08 Apr 2020
@ 08:16 am (GMT)

Nathan Foster

Re: Fascinating stuff - Projectile behaviour
Yes, always interesting. I dedicated a section of my book Small Arms Wound Ballistics to this subject (7.62 NATO section) with photographic evidence of the effect. But alas, this book is still under a semi restricted status. Given time, perhaps this will change.

In any case, as you say - worth considering as a factor in terminal behavior at close ranges.

As for range work or as a factor in long range accuracy, I only have one word to summarize this subject in its entirety: Bullshit.
08 Apr 2020
@ 03:13 pm (GMT)

Chris Murphy

Re: Fascinating stuff - Projectile behaviour
Looking closely it looks like it’s leaving the muzzle on the piss so there is some barrel/ammo issue there (stuffed barrel being and old tank or in concentric ammo ) this going to sleep shit people speak of they claim they shoot better groups at 200 yards than 100 cos the bullet settles down after 100 yards. For this to be true the bullet will have to be moving off it’s natural path. absolute bullshit
08 Apr 2020
@ 05:44 pm (GMT)

Apriori

Re: Fascinating stuff - Projectile behaviour
Quote:
Looking closely it looks like it’s leaving the muzzle on the piss so there is some barrel/ammo issue there (stuffed barrel being and old tank or in concentric ammo ) this going to sleep shit people speak of they claim they shoot better groups at 200 yards than 100 cos the bullet settles down after 100 yards. For this to be true the bullet will have to be moving off it’s natural path. absolute bullshit



As per my first post, there are a lot of unstated assumptions. IE projectile has not fully stabilised because the bore is worn, or it's a tank round in a sabot so is not perfectly concentric etc, etc, etc and there could be some sort of harmonics involved on the projectiles' X-axis. The video looked of interest and it's not something I've seen before.

Good to know that I was on the right track & the "going to sleep" theory is all bullshit.


Cheers!

AP

08 Apr 2020
@ 09:31 pm (GMT)

Magnus Vassbotn

Re: Fascinating stuff - Projectile behaviour
Hi.

In another post where accuracy related to this phenomenon was partly the theme, someone linked to a good test by Bryan Litz, where he concluded that improved accuracy at longer distance was most likely caused by either psychological or optical factors, and not the bullet starting to "home in" on the target due to stabilizing down range. A very interesting test. Recommended read.

Also, I guess that a lot of those claims of "progressive accuracy" come from a poor statistical foundation. People declare a certain accuracy at this or that distance, based on just a few groups. Litz was probably just too polite to mention this.


Magnus.
09 Apr 2020
@ 01:43 am (GMT)

Paul Leverman

Re: Fascinating stuff - Projectile behaviour
After all this time, at the range and in the field, I've had it right. Since hearing of this phenomenon and trying to wrap my head around it, I've checked various authors sources, slo-mo vids, range videos, physics text books, aerospace calculations, etc. Even though at first I mis-interpreted what was meant by "going to sleep", it turns out that it wasn't me. Everyone else was/is wrong. Each and every round that I shoot, no matter what calibre, velocity, bullet style and so on, "goes to sleep". The problem lies in the fact that all these experts and theorists are looking in the wrong place. All their calculations and observations are mistakenly made while the bullet is in flight. Mine, on the other hand, are fully stable and are "asleep" 100% of the time. The difference being that I observe and record my findings when the bullet has finished its job and is just laying there, on the ground or in the animal.
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