An incredible video on super, trans, and sub sonic bullets

[Scarlett Pistol]

https://youtu.be/BPwdlEgLn5Q

I had no idea about transonic being 0.8x to 1.2x the speed of sound.

[robert1804]

Excellent, thanks for the share!

[IDescribe]

I had no idea about transonic being 0.8x to 1.2x the speed of sound.

Just learned it a few weeks ago myself while looking something up related to boat-tail bullets and drag coefficient.  In the chart below, you can see highest point of drag at mach 1.2 and the lowest at 0.8.  One interesting thing in the chart is that the ranges where drag coefficient is most stable are mach 0.800-0.900 (900-1012 feet/sec) and  1.050-1.300 (1181-1462 feet/sec).

[Jiva]

This is very, very interesting. Thanks a lot for sharing.

[Wobbly]

Now that is pretty cool.

Same guy did another vid on riding a bicycle to demonstrate how the brain learns. That was way out there too.

[Scarlett Pistol]

I was really curious about the ?sub sonic? bullet (which turned out to be transonic) and how it looked like it was wobbling. That seemed rather unstable... Anyone know why it was doing that? Was it from the mid body transonic waves?

[newageroman]

I wasn't expecting it to be quite that cool but wow. UAH is local to me - lots of brainiacs over here. One thing he didn't mention is it looked like there were cloud twists due to the rifling. Awsome share, thanks.

[IDescribe]

I was really curious about the ?sub sonic? bullet (which turned out to be transonic) and how it looked like it was wobbling. That seemed rather unstable... Anyone know why it was doing that? Was it from the mid body transonic waves?

The bullet is traveling close to the speed of sound.  The air drags on it, and it drags on the air.  You have areas of low pressure and high pressure around the bullet.  You have air that relative to the bullet's velocity is accelerating and decelerating, and where you have areas that are particularly non-aerodynamic, like a cannelure in the bullet, the relative acceleration and deceleration of the air is magnified, and for a 300 Blackout doing 1080, some of that accelarating air  exceeds the sound barrier, and you end with a wave of compressed air coming off the non-aerodynamic section of the bullet.

I woukd have liked to have seen the a ladder with that bullet from 1080 uo to 1200, 15 feet/sec at a time, showing the bow wave starting to break up and the bullet passing through it.

[Scarlett Pistol]

Is the air accelerating at the tip  and along the ogive as the they are pushing the air aside? Thus the air accelerates? Then as the air transitions to and down the shaft of the bullet it decelerates? The shaft being where the cannelure would cause drag?

Are  the low and high pressure areas associated around the same areas due to what I tried to repeat back above. Dang, physics is suddenly even more interesting!

[IDescribe]

Is the air accelerating at the tip  and along the ogive as the they are pushing the air aside? Thus the air accelerates? Then as the air transitions to and down the shaft of the bullet it decelerates? The shaft being where the cannelure would cause drag?

No idea.  It's possible I even made all of that up.  Someone should check my references.   

[IDescribe]

Below is a picture of a typical cast lead bullet in supersonic flight.  It has the wave of compressed air in front -- the bow wave.  But you can also see it is producing waves off the lube grooves.





Now, in the video you posted, the subsonic bullet is not producing the pressure wave off the bow -- because it's subsonic, but it's still producing pressure waves behind the nose at points of poor aerodynamics, causing some air to accelerate back over the speed of sound.  My suspicion is that the one closest to the nose is a result of the sharp transition of ogive to shank, and the next one is a cannelure.  But I don't know.

[IDescribe]

Watch at the five second mark how that jet gets yanked on as it passes through the transonic range.

https://www.youtube.com/watch?v=hAFs7hTJKYo

[Scarlett Pistol]

That?s an awesome video.

[Wobbly]

The air drags on it, and it drags on the air. 

Thus, the constant lament of aeronautical engineers everywhere... "Air is such a drag."