Shooting in the rain

If the rain drop doesn't hit the bullet, then how do you explain the "clean" bullet hole? All the others have a black ring and that one doesn't....just a hole in the paper far away from the group.
 
Wilbur said:
If the rain drop doesn't hit the bullet, then how do you explain the "clean" bullet hole? All the others have a black ring and that one doesn't....just a hole in the paper far away from the group.
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Interesting that the errant hole is clean. I hadn't noticed this. Will have to look for it next time. Sure seems indicative of water on the bullet.
 
doghunter said:
As for the supersonic pressure wave, if anything deforms it, would not the resultant shock be passed back to the projectile and thus affect it?
* doghunter *
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Yes, that is logical, but the truth is that the Mach wave is not a magical brick wall that nothing can get through. If this were the case, then when you shoot a deer, the bullet couldn't penetrate, but only push the deer forward!
 
The pressure in front of the bullet pushed the rain drop into the target, and then the bullet followed it in.
 
Wilbur said:
As I wrote earlier, the probability of your bullet striking a rain drop is fairly slim. That statement is not of my own thoughts, but rather the result of some fairly exhaustive mathematics. If you shoot enough in the rain you're gonna hit a rain drop and the result is not likeable.

I'll say this and quit writing (yeah, really Wilbur), the probability of your bullet hitting a rain drop is fairly slim even in a moderate rain, but there is nothing physical involved - just the bullet being in the same place as a rain drop at the same time.
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On the other hand, in a heavy rain (I did the calculations for a 1" per hour rain) chances are that every bullet strikes multiple raindrops. This is what I found interesting at the Buckcreek match several years ago, instead of an errant shot once in a while, every shot was pushed in the same direction. What I think this shows is that in a light rain, you may hit a drop once out of several shots, pushing that shot far from the group, but for a heavy rain, each bullet is struck so many times that the POI becomes consistent again, but much different from the POI without rain.
 
mks said:
A common misconception. Air, water, whatever, flows through the Mach wave, which is just a transition in fluid properties, including pressure and density.
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Even air does not flow over a Mach wave.

The Bernoulli equation fails since it assumes a standing pressure wave cannot exist.
 
Skip the pistol part and go to the answer.

physics.stackexchange.com/.../how-does-a-hollow-point-...
 
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Some interesting thoughts here..........

How can an "Air Wake" ever be in front of a supersonic bullet? The word "Wake" would denote a phenomenon/disturbance AFT of the bullet.

And, a "Mach Wave" would have to also be aft of a SUPER-sonic bullet, no?

And finally; Can it REALLY be "raining buckets"....and NOT be "coming down hard"??? ;)

It was an interesting read, I was just pointing out some amusing statements, when you think about them, 'course, some were pro'bly

made in jest anyway. :D

I have seen rain on a trap range when its easy to see the passage of shot through a decent rain.

I watched on a fairly calm day, a .17 travel downrange numerous times and generate a disturbance that tapered in an arrowhead-like manner

behind it, all the way out to 300yds; And I wondered if, at the area just aft of the bullet, that disturbance wouldn't alter the pattern of the rain if

a rain would intrude in this area during a storm.

Fascinating experiences, though, thanks for the info. :cool:
 
From Wikpedia: "Shock waves can travel through any medium, including solids, liquids, gasses, and plasmas."

https://en.wikipedia.org/wiki/Shock_wave

Mach waves are cone-shaped, and extend outward from the bullet in all directions, including to the ground. If air couldn't flow through the wave, then the bullet would have to push an increasing mass of air along with it as it traveled from muzzle to target. It would be lucky to go a few feet before it accumulated so much resistance that it fell to the ground.

The same sort of Mach wave extends from a supersonic aircraft at 10,000 feet all the way to the ground. If planes had to push everything in its path in front of their Mach wave, they couldn't fly.

When we hear a sonic boom, the Mach wave has passed through our bodies. It does not push us to the ground.

The cloud of water vapor that many of us have seen when a bullet strikes a raindrop is not pushed by the Mach wave past the target. The Mach wave passes through it.

Enough examples?:)

Cheers,
Keith

No need to bring Bernoulli into this.:)

Added:

Here is a better reference for the mathematically-inclined: https://en.wikipedia.org/wiki/Rankine–Hugoniot_conditions

u2 in the first three equations (conservation of mass, momentum and energy) is the speed of air passing through the shock wave. u2 is not zero.
 
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At The Nationals in Phoenix several years ago, we had a sudden rain storm come in during my relay. The rain was not blowing under the firing line awning, it was just a steady downpour.

I had a shot go almost ONE INCH off from my group. This was at 100 yards.

This is not the first time I have had this happen.
 
Very easy just go to the above third icon from the right (insert image) click on it and do as it says. First click on the below (reply to thread) icon.
Chet
 
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IMG_0390.jpgIMG_0390.jpg

The shock waves are different on H P Versus a pointed bullet, but in my opinion if it is raining hard enough and the distance is "100 Yards" both bullets will be deflected if the raindrop hits it. The weight of the bullet 68 grain should deflect more than a 168 grain

I M H O
 
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mks said:
From Wikpedia: "Shock waves can travel through any medium, including solids, liquids, gasses, and plasmas."

https://en.wikipedia.org/wiki/Shock_wave

Mach waves are cone-shaped, and extend outward from the bullet in all directions, including to the ground. If air couldn't flow through the wave, then the bullet would have to push an increasing mass of air along with it as it traveled from muzzle to target. It would be lucky to go a few feet before it accumulated so much resistance that it fell to the ground.

The same sort of Mach wave extends from a supersonic aircraft at 10,000 feet all the way to the ground. If planes had to push everything in its path in front of their Mach wave, they couldn't fly.

When we hear a sonic boom, the Mach wave has passed through our bodies. It does not push us to the ground.

The cloud of water vapor that many of us have seen when a bullet strikes a raindrop is not pushed by the Mach wave past the target. The Mach wave passes through it.

Enough examples?:)

Cheers,
Keith

No need to bring Bernoulli into this.:)

Added:

Here is a better reference for the mathematically-inclined: https://en.wikipedia.org/wiki/Rankine–Hugoniot_conditions

u2 in the first three equations (conservation of mass, momentum and energy) is the speed of air passing through the shock wave. u2 is not zero.
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If a Mach wave enters a jet engine inlet the engine is instantly choked off from the interruption of air flow.
The idea that the mach wave extends to infinity and represents an infinite load is grossly wrong in concept.
Over a limited area it is a standing pressure wave.
The pressure difference drops across the wave as you move away from the supersonic object.
Air flows AROUND the roughly cone shaped pressure wave, but not through the wave.

As velocity increases the Mach waves forms and attaches to the object.
It IS in front of the object at the front. How far depends on the density of the 'fuid' the object is moving in.
As velocity continues to increase the Mach angle (opening angle of the Mach wave that face backwards) becomes smaller and actual drag force declines.

Chuck Yeager was the first one with enough balls to go above Mach 1.
The other pilots tried to creep up.
Control force increased and buffeting occurred as the Mach waves attached.
The Mach waves had to be moved along with the control surface.

Even now we fly below Mach 1 or above Mach 1 (with some margin on each) but not AT Mach 1.
 
When flow is choked, it has reached a maximum that cannot be exceeded without changing the upstream conditions. The flow does not suddenly stop.

https://en.wikipedia.org/wiki/Choked_flow

The second equation gives the mass flow rate through the shock wave under choked conditions.

Again fluids, including air, flow through a shock wave, whether it is around a bullet or in a venturi.
 
mks said:
When flow is choked, it has reached a maximum that cannot be exceeded without changing the upstream conditions. The flow does not suddenly stop.

https://en.wikipedia.org/wiki/Choked_flow

The second equation gives the mass flow rate through the shock wave under choked conditions.

Again fluids, including air, flow through a shock wave, whether it is around a bullet or in a venturi.
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Air does not flow over a shock wave.
That is the very definition of a shock wave in a compressible flow.

We sepent a lot of effort to keep the Mach wave out of the inlet of the SR71 engines a long time ago.
They mostly operated as bypassed ram jett.
The air flow choked instatly if the mach wave entered the inlet.
It made for spectacular pictures of flames from teh afgterburner.
they are very common pictures.

The computer (originally analog) immediately commanded full rudder to counteract the loss of thrust from an 'unstart' from the choked flow.
A pilot would never react fast enough to maintain control.

They complained about their heads striking the inside of the canopy the motion was so violent.

I have denstrated chocked flow for at least the past 20 years in my lab to undergrads.

I increase the pressure driving a gas though a small tube higher and higher.
The tube is instrumented with all sorts of mass flow, velocity, and pressure sensors (the purpose of the class is instrumentation).
As the flow speed increases the tiny perturbations the sensors create allow Mach waves to attach.
At the critical speed the pressure shows a step over a short distance, the mass flow drops to zero.
The tube is still open but the silence is deafening.
No more screaming gas.

If there is time we repeat it using a nozzle shaped to increase flow speed through a throat.

Part of the deonstration is to make sure students stay alert to how sensors can disrupt the very target of measurements.
 
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I understand that it is difficult to reconsider a long-held belief, but please have a look at this short lesson on choked flow:

https://www.youtube.com/watch?v=DNURRIJz94k

At the 3:17 mark, the instructor shows a graph of mass flow rate as a function of back pressure. You see that mass flow rate is maximized when choking occurs at Mach = 1. Later he shows simulations of flow through the shock wave for different back pressures.

Here is a video in a supersonic wind tunnel of flow through a shock wave:

https://www.youtube.com/watch?v=BI7R8KiX8HU

Not only is there flow through a shock wave, flow is necessary for a shock wave to occur. The shock wave occurs where Mach = 1, i.e., where the speed of the air is equal to the speed of sound.
 
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