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Bullet shockwave footage
- Thread starter sam1700
- Start date
In the revolver video the recoil impulse is way behind the bullet leaving the barrel. Wish there were some reference marks behind the revolver to note its position through the firing.
I was getting smarter up until the point he recommended Ben Sasse than I became irretrievably dumb.
You can use that type of photography to look at all types of movements in the air. The first I ever saw use of it was to show gas escaping from a coke bottle. When you hear that hiss, you don't see the goddamn mushroom cloud it makes! It's pretty cool.
About half way between the front and rear of the super sonic shock wave, you can see the spiral caused by the rifling
Nice imaging set-up. He did not mention how he triggered the high-speed video camera though. I hope my bullet design flies a lot cleaner than that 50-caliber bullet. I expect it to produce major bow wave and base shocks, and minor ones only at base of ogive, start of rear driving band, and start of the boat-tail. Notice the persistence of the wake vortices in the videos. That bullet has a lot of base drag. There was not enough resolution to see the boundary layers. Also, many things are happening in the muzzle-blast zone. First, you saw the Mach 1 shock of the air compressed ahead of the bullet in the bore. Those refracting muzzle-blast shocks are exactly why optical triggering chronograph screens must be well downrange from the muzzle in order to trigger reliably on bullet passage. The aero instructor's comments on the shocks around the "subsonic bullet" are correct, except that the Mach 0.8 to 1.2 transonic airspeed range really applies to tangent ogive bullet designs. Secant ogive VLD bullets experience transonic effects only from about Mach 0.9 to Mach 1.1. It is not actually the speed of the bullet relative to Mach 1.0 which determines whether a supersonic shock is produced. It is the highest speed of the air flowing around that bullet which is determinative. Blunt meplat revolver bullets have to be going well below Mach 0.8 in the ambient atmosphere to avoid producing a sonic crack sound. By the way, the speed of sound in air varies primarily with the square root of the air temperature on an absolute temperature scale (degrees Kelvin or Rankine). It is a lot slower on a cold day.
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Awesome video! I love watching this stuff where we see what's actually going along with the bullet.
I assume the acceleration of the air is not even around the top and bottom of the bullet, and in the video it appears there are larger sick waves off the top. I assume this would cause flight instability and deviations?
That is an interesting point Jim,. I can see that because of more total surface area on the tangent ogive the air would be moving faster than a secant ogive. I have to ask though, how does the sharper angle of ogive to bearing surface on a secant affect airspeed around the bullet? It's more of a disruption that is for sure. Like a smooth surface of an aircraft going mach II, then change a contour it makes a huge difference.
Just sarcasm my friend. Although I think ICE would like to see sort of proof of citizenship from that "professor".
Bullet designers usually try to minimize the TOTAL AERODYNAMIC DRAG of their bullets when they are flying at about Mach 2.5 with zero angle-of-attack. The total drag is comprised of meplat drag, headshape drag, skin friction, driving band drag, and base drag. For example, truncating the long pointed nose of a ULD bullet by 0.200-calibers adds some meplat drag, but reduces skin friction drag by even more.
Minimum supersonic drag headshapes include Sears-Haack Lowest Drag and Secant Ogives with RT/R=0.50. The secant ogive used is exactly midway between a tangent ogive and a conical ogive at each particular non-truncated nose length. The two minimum drag nose shapes bleed off the bullet's initial kinetic energy at a slower rate while generating the supersonic bow and ogive-base shockwaves. While the Sears-Haack LD headshape is theoretically best, the secant ogive can be just as good in actual practice.
Maybe it was just me but the sub seemed to have a nose-up attitude with relation to the flight path. Not quite stable perhaps?
If one looks carefully at the Schlieren video of the shocks exiting the muzzle of the rifle barrel during firing, one can observe the gas leakage past the bullet within the barrel exiting ahead of the bullet itself. The bullet is going at about Mach 1.2 at the time of peak base pressure behind it. The small Mach 1.0 shock wave of compressed air ahead of the bullet exits the muzzle first. One can see its small vertical plane out front. Better bullet obturation using copper ELR bullets is the subject of my latest paper (attached below). After publishing this paper two days ago, I discovered that QuickLOAD actually calculates the base pressure behind the bullet as it travels down the barrel, and corrected the paper accordingly.
Jim Boatright
Jim Boatright
Here is a picture of some base-drilled and undrilled bullets recovered from a swimming pool. The top bullet is unfired. The next one was not base-drilled. Note the large gas leakage paths in the groove edges. The lower two bullets were base-drilled to the depths indicated by the black annotation marks. Note the clear evidence of bullet expansion with base pressure being ported internally and the much better gas sealing. The test barrel was a 6-groove Krieger, conventionally rifled at 10-inches per turn. Water impact was at 3000 fps at a 45-degree angle of incidence. The noses curled over more at higher impact speeds.
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