Home Forums Hunting & Shooting Ask The Gunwriters Bullets Corkscrewing Along Trajectory

A few days ago, I had cause to do some digging on this topic. It seems like something worthwhile reporting here. Enjoy:

My main source is Harold Vaughn's Rifle Accuracy Facts. Harold was in charge of handling the fluid dynamics computations for our country's ICBMs, and he held a doctorate in the field. He was also a hard-core experimentalist, dragging a big old Tektronix 555 oscilloscope (I had one of those once.) and gas generator into the field to make measurements. If you want to understand how his work is regarded, try buying a used copy somewhere.

Question 1: Does the nose of the bullet trace out a spiral as the bullet flies? Yes. Harold developed software that accurately models the situation. The software is capable of six degrees of freedom, i.e., it handles position in three dimensions and angles in three dimensions. Here is one of the graphs he produced.



Question 2. Does this cause the bullet to corkscrew around its trajectory? Yes. It must be so, because the bullet is "coning" and the drag vector always points from tip to center of base. When the bullet nose does not point exactly along the trajectory, the drag vector has a transverse component that moves the bullet sideways and up and down. Fluid dynamics substantially changes the situation, vs. ballistics in a vacuum.

From page 182:


Question 3. Is this effect important to most of us? No. From page 192:


Bryan Litz's money (he issued a challenge for anyone to show a rifle more accurate at 200 yards than at 100) is probably safe unless someone with a lot of patience and a superbly accurate rail gun chooses to compete for it.

Awesome post! This is what I love this place!

Bookmarked.

It's "corkscrewing" around an imaginary mathematical point.

The graph is misleading since that's not the bullets path.

It's the motion of only the tip and it all occurs in fractions of a second.

Not really.

There is nothing imaginary about the centerline of the trajectory. It's real. I can tell you what it is and where to find it.

There is nothing misleading about the graph. It's clearly labeled as the pitch and yaw of the bullet.

The corkscrewing is a consequence of the pitch and yaw. It is real motion of the center of mass of the bullet around the centerline.

One of the first, and I thought one of the coolest, articles I can remember reading in one of my cousin's American Rifleman was about this very topic. There was a drawing that looked like a drawing a kid would make with a Spirograph toy almost like petals of a daisy similar to the one in the OP.

I've been hooked ever since and that was probably around '62, age 12.

And the drag induced by the pitch and yaw of the bullet passing through the atmosphere. As was pointed out, this motion would not occur to this degree in a vacuum.

Yes!

If you could somehow magically turn the nose of the bullet by say half a degree to the right, and hold it there, the drag vector would have a leftward component, and pull the bullet to the left.

Denton,....GREAT POST !

.......There's absolutely NOTHING that compares to having good rested eyes, and a quality optic,....while spotting / coaching for a well trained and capable rifleman, on a cool damp early summer morning, with the sun at ones back.

The given being that your accomplished, "Across the Course / 1000 yard = / F class shooter has loaded his ammo to either be sub sonic, or still supersonic anywhere's CLOSE to the target he's ranging in on. "Going through the wall", just prior to hitting, PARTICULARLY at ranges beyond 500 M. is bad mojo.

It's just awesome watching the trace enlarge and leave that "corkscrew" and than "go back to sleep, and drop RIGHT INTO the 10 and X ring.

The Ranges at Raton are SUPERB for this ,....particularly with the big BPCR and BPLRT guns and loads.

Love to shoot,....I mean LOVE it,....but'spect I might enjoy spotting almost as much,....maybe even a touch more.
....and I love either in a howling switchy gale of wind, too.

GTC

I'll be first: at least 4 pages but no more than 6.

...yup, and one of the reasons that a well qualified spotter will ask his shooter whether he's shooting a right, or left hand twist barrel, right off the bat.

GTC

Mr D

A very interesting read and enjoyable. Thanx for kicking it off.

Jerry

I'd love to see high speed video of this phenomenon.

Thanks Denton,

But how dare you bring science to the 'fire.

Next you'll be attempting to prove that the bullet doesn't rise when it leaves the muzzle.

Geno

I'm reminded of the story about someone who claimed that a curve ball is an optical illusion. Some pitcher said that he should go stand behind a tree and he'd kill him with the illusion of curve balls.

So how does this pencil out in inches of deflection on the x and y axes?

I do find it a little odd that the pattern is essentially round. I would think gravity might alter things into more of a vertically shaped ellipse.

I like the sarcasm.......we all know the bullet has a mid trajectory arch

Jerry

About plus and minus .009" for the example shown, close in, diminishing to plus and minus .003" farther out.

If this is your biggest accuracy problem, I'm impressed.

Thanks. Now that I have wind and gravity mastered. I'll start taking that into account the next time my Sharps goes to the 1K line.