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Forum Index > Rifles general discussion > Didn't we see something about this.....

Didn't we see something about this.....

01 Jan 2018
@ 06:12 am (GMT)

Paul Leverman

From another forum:

"In a perfect world (no wind) you’d think that doubling the distance would double the group. It seldom works that way. When the bullet leaves the muzzle it rarely flys exactly true, the bullet is likely not perfectly stable, there is a certain amount of wobble. The longer the bullet travels the more error in the intended path. The only exception to this is the behavoir of Very Low Drag (VLD) centerfire bullets. Due to their length they may need a few micro seconds after leaving the muzzle to fully stabilize. In this case the 200 yard MOA may be better than that at 100 yards. That does not mean the 200 yard group is smaller, it means the 200 yard group will be less than double the 100 yard measurement. Wind is also a huge factor. The longer the range the bigger the wind factor."

So, what he is saying is that after the long VLD stabilizes, it veers from its established trajectory and corrects itself by changing the angle of flight, back to where it was originally pointed before it started to wobble.

I'm trying to picture this and I see two identical bullets, fired at the same time, leaving the muzzle and flying perfectly parrallel to each other. Both are "wobbling" in the exact same manner, both are veering from intended flight path the exact same amount (MOA), and yet one of them is able to overcome inertia and acceleration and re-orient itself to the aim point at the 100 yard mark. How is this possible? Unless, he is referring to the wind factor, where the bullet travelling to the 200 yard mark has decelerated, giving the wind more time to push it back onto its intended flight path, seemingly "correcting" its errant flight path.

I don't buy it.

Replies

01 Jan 2018
@ 06:33 am (GMT)

John Smith

Re: Didn't we see something about this.....
I'm with you.
01 Jan 2018
@ 07:00 am (GMT)

Bob Mavin

Re: Didn't we see something about this.....
Like making two paper planes, one will glide straight the other may be crap ??

Or playing darts with no flights?
01 Jan 2018
@ 07:06 am (GMT)

Bob Mavin

Re: Didn't we see something about this.....
Woops!! Maybe the barrel harmonics differ between projectiles, If the projectile exits the bore at the same point of vibration each time.

Bob
01 Jan 2018
@ 08:33 am (GMT)

Ed Sybert

Re: Didn't we see something about this.....
I think that the term describing how some long (perhaps VLD) bullets can exhibit tighter MOA at a longer yardage than at a shorter one is:
Precession-

Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In other words, if the axis of rotation of a body is itself rotating about a second axis, that body is said to be precessing about the second axis.

This may be the wrong term but it's what comes to mind at this time. The bottom line is that the bullet can take some time to stabilize.

20-odd years ago I had a .223 target rifle built especially for 80 grain Berger VLDs. It had a fast twist barrel appropriate to that bullet length. It did hold tighter MOA at 200 yards and beyond than it did at 100 yards.

Happy New Year to All
01 Jan 2018
@ 08:56 am (GMT)

Joshua Mayfield

Re: Didn't we see something about this.....
I wanted to believe in this. I think it was Bryan Litz that called this "epicyclic swerve" and did testing that did not support the notion. I liked the idea, not from shooting, but from throwing a (American) football. Before I wrecked my throwing shoulder I could throw a ball that would have some initial wobble but would stabilize in its downward path and carry further than expected. At least that was my perception and watching the ball carry over the defender who thought he was in position supported my belief. I wanted to believe the same was possible with bullets, especially when I wasn't happy with my 100 yard groups. But Litz' study was pretty convincing to the contrary. I'll try to find the link later. Duties of the pater familius are demanding that I close this post for now.
01 Jan 2018
@ 09:14 am (GMT)

Warwick Marflitt

Re: Didn't we see something about this.....
So if you fire same said bullet over 100 yards of 50deg day hot ground through hot thin rising air . Then fire that same JFK styled bullet over the same distance at the same altitude over -50deg Frozen cold thick dense air what would the difference in atmospheric conditions have on the wobbling Ozwaldations and presidential impacts of placements. I'm going to play the Trump card !!! FAKE NEWS..... better to reload some partitions and get out hunting meat for the freezer than worry about wobble bullits
01 Jan 2018
@ 09:31 am (GMT)

Paul Leverman

Re: Didn't we see something about this.....
Interesting, Ed. So, correct me if I am misinterpreting this. It sounds like what is happening is that the one "wobble" will finally settle into rotational stability, but while that rotational axis is satisfied and balanced, a second rotational deviation begins/takes over, thus creating a second "wobble" of a different frequency, and in time this second harmonic will also stabilize, and probably, so on and so forth. If this is the case, I can see this happening, and am good with that. But, how could this phenomenon result in the bullet path actually changing direction with predictable results? In my mind, each and every bullet of choice would have to be so close to perfect or identical in nature for this to occur with any regularity.
And once the bullet had "corrected" itself on the path to the POA, why wouldn't it continue on that secondary trajectory indefinitely. It seems, to me anyway, that once the new course had been plotted to arrive at the POA for say 200 yards, it would still need to be changed yet again for 300 or 400 etc.

01 Jan 2018
@ 09:38 am (GMT)

Nathan Foster

Re: Didn't we see something about this.....
I very much dislike this type of thread due to the fact that it brings out a lot of bogus input. Nevertheless, you are quite right Paul. I went over this in the book series.

Put simply, it would break the laws of physics to have a rifle that groups say 1.5" at 100 yards but 1" at 200 yards. Precession cannot be factored into this nonsense. To have groups smaller at 200 yards, the bullets would each have to change direction. This is very basic physics.

I see too much of this pontification among long range shooters, looking for answers (excuses) to inconsistencies in their field work. Yes, you may have smaller groups at 200 yards than 100 yards, but this has nothing to do with the load. It is the shooter that is the problem. Don't be sucked into this myth, it has been bandied about for far too long.
01 Jan 2018
@ 11:13 am (GMT)

Lane Salvato

Re: Didn't we see something about this.....
"The Practical Guide Series" would seem an apt solution to all of these problems. Or am I making it too simple?
01 Jan 2018
@ 03:08 pm (GMT)

Paul Leverman

Re: Didn't we see something about this.....
Yes and no. There is nothing wrong with an open discussion of ideas, always willing to discuss for or against anything. (I have an opinion about everything, just ask me.)

When I read that statement on the other forum, my first thought was of Nathan's passage about the bullets that defy the laws of physics. But the poster had said it with just enough air of certainty and factual presentation that I just had to bring it here. He was right about some aspects, such as the beginning statements about bullet flight, but then he veered from reality to myth. But he did come back for a short stint when he talked about the importance of the wind and its effects.

I'll be so glad when we can get back shooting again. I know that Hodgdon says their powders are temperature stable, but I really don't feel like testing the hypotheses at -36*C.

02 Jan 2018
@ 12:42 pm (GMT)

Joshua Mayfield

Re: Didn't we see something about this.....
Here is the piece I mentioned above on epicyclic swerve. I reread it and if you don't feel like reading it his point is (after extensive study) that whatever it is that leads to tighter angular groups at longer ranges for some shooters, it is not epicyclic swerve or the bullet going "to sleep." All this points toward the probability that Nathan is right, again. Which is annoying because I'd love to have something fancier than the shooter to blame my subpar 100 yard groups on.
02 Jan 2018
@ 12:50 pm (GMT)

Joshua Mayfield

Re: Didn't we see something about this.....
Woops, here it is.
http://www.appliedballisticsllc.com/Articles/ABDOC104_EpiciclicSwerve.pdf
02 Jan 2018
@ 06:23 pm (GMT)

Paul Leverman

Re: Didn't we see something about this.....
Interesting read, Joshua. Pretty well sums it all up.
02 Jan 2018
@ 06:27 pm (GMT)

John D. Hays - New Mexico

Re: Didn't we see something about this.....
I’m with the nay-sayers on this. Trig and physics are against it. It just sound like folks trying to make scientific sense of the efficacy of using divining rods to find underground water. The real explanation is in differential input, psychology, chance, and confirmation bias.

Aim small, miss small —- isn’t that the mantra? Don’t we tend to aim smaller and take greater care at longer distances? If we dismiss the 1+ MOA groups at 200 yards and rejoice and wonder at the sometimes sub-MOA groupings aren’t we just marveling at random sampling error (maybe with one or two “excused flyers”)? I am with Nassim Talent on this kind of thing. Black Swans happen.

With enough of a sample size, the established physics would be supported and the occasional 200 yard sub-MOA groupings would be shown as statistical outliers.

“Reversion to the mean” does not imply that bullets in flight choose to swerve to nail a black dot on a paper target just to gratify a shooter.

This isn’t Zen and it isn’t quantum physics. It’s the science of ballistics.
 

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