Vapour Trail
- Thread starter Buckmastr
- Start date
I missed the part about the oil. I figured centrifugal force alone would still cause and evenly expanding trail more like this,
- Location
- Southern Vancouver Island
High rotational speed along with the rifling impression on the projectile from the barrel acts on the air much the same as a boat propeller in water. It's a form of cavitation that be visible to the naked eye when conditions be right. Fluid Dynamics at play.
If it’s caused by the rifling impressions why one though? That would be like a single blade props pattern. There would be an equal number of trails to grooves like how there’s cavitation at the tip of each blade on a propeller. The cavitation of a prop viewed from the rear like the original picture would look like expanding circles, not a single corkscrew trail.
4 blades, 4 sources of cavitation. No doubt that is happening but doesn’t account for the shape of the smoke which rrh1 brought up in my opinion. Think the left over lube smoke is just being curled by the forces of the bullet.
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This video from the YouTube channel "Smarter Every Day", will provide some insight. Super-slow-motion video of rifle bullet shock waves which radiate outward as a perfect cone, and the vapour column that stays linear thinly compressed behind the bullet until it gradually expands, but only slightly. Its super-clear in the video.
The vapour trail is spinning as its generated. I am guessing the OP photo was taken on a zero wind cold morning where the muzzle blast smoke and the vapour trail had time to hang a long time in the air before dissipating.
The closer to the muzzle, the longer the vapour column has to move via its centrifugal force in the still air surrounding it. If we could measure the outer diameter of the corkscrew vapour column shape, I think we would see that it tapers from wide to narrow from muzzle to target, because of the flight time differential.
Slightly off topic, but starting at 8:36 in the same video, you will see how incredibly leaky a revolver blast is. There are shock waves and gasses blasting out all over!
The vapour trail is spinning as its generated. I am guessing the OP photo was taken on a zero wind cold morning where the muzzle blast smoke and the vapour trail had time to hang a long time in the air before dissipating.
The closer to the muzzle, the longer the vapour column has to move via its centrifugal force in the still air surrounding it. If we could measure the outer diameter of the corkscrew vapour column shape, I think we would see that it tapers from wide to narrow from muzzle to target, because of the flight time differential.
Slightly off topic, but starting at 8:36 in the same video, you will see how incredibly leaky a revolver blast is. There are shock waves and gasses blasting out all over!
