Why do pellets "corkscrew" ?

I've seen this in some videos and from my understanding it usually happens with .177 or .22 being overpowered. The lighter pellets traveling at too great a velocity will encounter to much air turbulence for the weight of the pellet causing this effect. Now that I think about it Ted covered this in one of his videos.

There are a few threads here about it as well.

what gun are you shooting? what pellet? what caliber? what speed?

A dirty bbl. is often the culprit or just the wrong pellet for the gun. Also as FastEddie stated, over powering a pellet can cause it to be unstable. I recall an article on muzzle loaders where over powering caused the base of a soft lead bullet to mushroom. I wonder if over powering pellets causes the skirt to deform?

Spiraling Pellets - Nemesis of Air Rifle Accuracy ​

I now have a ready-made reason for misses and fliers. I'm new to air gunning and didn't know about corkscrewing. 

Thanks for posting the video.

These are the major problems...The first two are detrimental and the third sometimes is corrected after the bullet has reached some distance...

The "Corkscrew" is known as "Precession" ....Secong pic shows the cause for this.

The "Nutation' you can see in much in videos from the military shooting machine guns, etc...The circling sometimes gets smaller with distance while the bullet is finding its stabilizing mode.

https://imgur.com/eCFsfFN

Regards,

AZ

PS. Love your Dune Bug...Is it Meyers Manx over a shortened VW chasis?

I finally found it! I stumbled upon it years ago and luckily is still online. This is a nice flash "simulator" showing this precession and nutation effect. http://www.arld1.com/nutation.html
There are LOTS of other cool "simulations" too to understand better the theory behind airgunning.

That simulation is neat, but what actually causes this behavior? I've heard that commercial pellets are swaged from lead wire that may contain tiny voids or impurities, which would unbalance them. But this could just be marketing hype from people who want to sell you a pellet mold. A lot of people believe that pellet size makes a big difference, with oversized pellets being more likely to spiral. This seems like a sound theory. I've seen photos of oversize pellets pushed through a barrel where the rifling was clearly cut deeper on one side of the head, or the skirt was damaged in an asymmetric way by the choke or crown. A pellet damaged like that would tend to veer off to one side, but the fact that it's spinning keeps it in a spiral. A pellet with a thin skirt could probably also be bent if you seat it in the chamber by pushing on the skirt instead of using a probe to push it in by the head.

It is know that too large of a pellet head diameter causes the cork screw flight. Even a too small head diameter isn't as bad as one that is too large. Also I have read that too high a velocity causes tumbling of the pellet. That's why I think you see reports of poor accuracy using PBA pellets. 
When a pellet doesn't fly properly, you see really bad groups..like 3" at 50 yds. Even a too small head diameter isn't as bad as one that is too large. 

The biggest reason for a pellet to corkscrew, is that the head size of the pellet, is either too big or too small for your barrel.

I have a Steyr LG110 FT. I had great accuracy at short range, from like 10 to 25 yards. My best groups at 50 yards were like 5" to 10" group. At first I thought the barrel was dirty, and I would clean it untill I got a clean patch. Unfortunately it had no effect.

The pellets that I was shooting had a 4.52 head size diamator

then I saw the pellet sorting that Ted Bier did on Youtube, I went and bought different head size pellets in JSB. 4.50, 4.51, 4.52.
The berrel had it's best accurate groups with the 4.50 pellets. Now I shoot sub .2" groups at 50 yards.

Finally I have the accuracy that I have been expected from my rifle.

Biagio