Physics of shooting a rifle

[georgehwbush]

david (https://thefiringline.com/forums/att...1&d=1723906688)

i like the photo you posted, it shows gases influence farther away from the muzzle than the bullet, thus proving that supersonic flow of gases from the muzzle is possible. nice move. <check/>

not only are they further than the bullet, but they had to change dirrection to get there. those little atoms are in a hurry !

one other thing, i didn't notice anyone mention the compressed air in front of the bullet which exited ahead of the bullet, at supersonic speed of course! which will have an affect on the bullet when it has to pass through that MESS.

 

[davidsog]

Mass Flow, John....

You think I claim air does travel at supersonic speeds. I never said that. I said normal shock does not flow any faster than the speed of sound.

Once again, you do not understand shock wave formation or the characteristics of shock waves.

As for your big revelation of mach diamonds forming a chain....

What do you think "and the process starts again".

Nowhere in a mach diamond does flow cross a normal shock at supersonic speeds or at any speed other than extremely low energy separated flow.. Nowhere, John....

 

[davidsog]

I will try and explain characteristics of shock waves for you. That might help out. Give me a few days as I am at work putting these concepts in action, ??????

 

[JohnKSa]

You think I claim air does travel at supersonic speeds. I never said that.

Exhaust gases exiting the muzzle cannot travel faster than the speed of sound and they almost instantaneously adhere to that once they exit a confined space.

There is no a 5000fps movement of gas once it escapes the muzzle.

Instead, the motion becomes a vibrational wave which is the basis of normal shock. That vibration is speed limited by the speed of sound.

The gas at exit can only travel at the speed of sound at the local flow level. The bullet is traveling much faster than that.

To be very technical in any supersonic flow, there is a tiny portion that does exceed the speed of sound in some cases. It is very localized flow close to the body just before the normal shock depending on the shape of the body in flight. It get roughly mach 1.2 and represents air molecules being shoved out of the way by the shape traveling thru the air mass.

For the third time on this thread. What sort of game are you playing? Why would you say one thing multiple times and then try to pretend that you didn't?

I will try and explain characteristics of shock waves for you.

No.

FIRST, you explain why you have repeatedly claimed that muzzle gases can't travel faster than the speed of sound in air and/or faster than the bullet when clearly they do.

I provided a technical source that proves they do (1900m/s) and explicitly states that they catch and impact the bullet and you completely ignored it. As in totally failed to acknowledge its existence.

Hatcher measured them traveling several times the speed of sound in air--4700fps. You have completely ignored this fact.

Muzzle crown issues that don't touch the bullet and still cause accuracy issues prove that they do. You tried to discount this saying it wasn't a normal case--which is true--but not relevant since it proves that the gases do affect the bullet in spite of the fact that you say they can't catch the bullet and in spite of the normal shock which you claim prevents that.

IF you have changed your mind about muzzle gases being able to travel faster than the speed of sound in air:

1. Please have the common courtesy and decency to explicitly state that fact in clear English rather than trying to pretend that you never made the claim in the first place. It would be nice if you could explain where the confusion arose that caused you to make multiple contrary-to-fact assertions.

2. You posted charts and pictures and sources to support your assertion. If you have any integrity (personal, professional, technical), and your goal is to share knowledge and inform, you will want to explain how and why you took those plots out of context, and/or misunderstood/misinterpreted them so others will not make the same mistakes.

3. Stop arguing the point. Once a point is settled, there's no need to keep arguing as if it's not settled.

Then we can move on to the next topic. There's no point in having multiple balls in the air at once.

 

[Unclenick]

Think of the propellant gas molecules as little bullets at a higher temperature (higher average kinetic energy) than the surrounding air. This is what enables them to exceed the speed of sound as they blow out of the muzzle and into the outside air. As soon as interaction with that air has depleted enough of their kinetic energy, they drop to the same temperature as the outside air. This takes a little travel distance and time. The shockwave they create propagates outward, and after the first couple of feet, it is going no faster than the speed of sound in outside air. It might make an interesting analog to the rapid expansion period after the Big Bang.

 

[davidsog]

There is no guesswork as to the speed of the air in a normal shock.

I will be back on to try and help you all to understand what is going on.

It is a physical property of the normal shock that the velocity of the air is fixed. There is only one tiny tiny portion that exceeds the ambient speed of sound and it no faster than Mach 1.2 at its greatest speed. The velocity of the air reaching the ambient speed of sound IS the Normal Shock. Immediately behind the Normal shock, the velocity of the air is zero. From there it picks up speed but it does not become supersonic or faster than supersonic without oblique and expansion shock.

Those two shock waves add velocity that can exceed the ambient speed of sound but wherever a normal shock is seen.....
The air is moving no faster than the ambient speed of sound.

That is how the physics works.

No amount of speculation, conjecture, or posturing will change the physical properties of Shock Waves.

Normal Shock is ALWAYS MACH 1 and the air behind it subsonic. There is no physical possibility for anything to influence anything UPSTREAM of a normal shock.

 

[davidsog]

FIRST, you explain why you have repeatedly claimed that muzzle gases can't travel faster than the speed of sound

I never said gases cannot travel faster than the speed of sound. I said they do not travel faster than the speed of sound in a Normal Shock and in the atmosphere they do not do so for any distance without lots of mass flow. A gunshot does not have the mass flow to be able create a supersonic stream of air for any distance. It does impart a very energetic vibration like all explosions do....

Stop taking my original statement out of context from the discussion of a bullet exiting the muzzle of a gun......


You understand that the air is not moving around the bullet but rather the bullet is moving thru the air. If it was not for the bullet being there...
There might be a tiny portion of supersonic air exiting the muzzle. As it stands, the Normal Shock of the bullet prevents any significant disturbance coming from anything DOWNSTREAM of the bullet to enact UPSTREAM influence over a Normal Shock.

The properties of Normal Shock are immutable laws of physics. Not understanding that does not change it.


Those thick lines at the front and the rear of the bullet ARE Normal Shock:

You can also see the "Pressure Shell" as the author of the high speed photo article called it formed by the bullet as it encounters the atmosphere. That is a very accruate description despite its not being very technical.

 

[JohnKSa]

I never said gases cannot travel faster than the speed of sound.

You absolutely claimed several times that the muzzle gases could not travel faster than the speed of sound. You also stated that they were going much slower than the bullet.

I will provide these quotes again.

Exhaust gases exiting the muzzle cannot travel faster than the speed of sound and they almost instantaneously adhere to that once they exit a confined space.

Note that you absolutely did say they can't travel faster than the speed of sound.

There is no a 5000fps movement of gas once it escapes the muzzle.

Instead, the motion becomes a vibrational wave which is the basis of normal shock. That vibration is speed limited by the speed of sound.

Note that you did say that the muzzle gas movement was limited to the speed of sound in air. But it clearly is not.

The gas at exit can only travel at the speed of sound at the local flow level. The bullet is traveling much faster than that.

Note that you claimed the bullet was traveling much faster than the muzzle gases but, in fact, the gases are traveling much faster than the bullet when they exit the muzzle and, as the source I provided proves, they do catch the bullet.

To be very technical in any supersonic flow, there is a tiny portion that does exceed the speed of sound in some cases. It is very localized flow close to the body just before the normal shock depending on the shape of the body in flight. It get roughly mach 1.2 and represents air molecules being shoved out of the way by the shape traveling thru the air mass.

Note that you did state that only a tiny portion of the gases could travel fater than the speed of sound which is not true. The muzzle gases exiting the muzzle are initially traveling several times the speed of sound in air (not "roughly mach 1.2) and stay supersonic for a non-negligible distance.

In fact, you are still making the claim. I have to say, this is pretty remarkable--you are claiming you didn't say something that you clearly did say and at the same time re-iterating the point and arguing in support of it. Quite a novel debate technique.

There might be a tiny portion of supersonic air exiting the muzzle.

Wrong. The muzzle gases exit at several times the speed of sound in air and stay supersonic for a non-negligible distance.

You understand that the air is not moving around the bullet but rather the bullet is moving thru the air. If it was not for the bullet being there...

You are trying to change the subject. This is about the muzzle gases and very clear and specific claims you have made about their speed on exit and their behavior after exit.

That is how the physics works.

If you believe that physics prevents the muzzle gases from exiting at several times the speed of sound and from traveling at supersonic speeds for a non-negligible distance, then you don't understand the physics because physics does not provide information that is contradictory to real-world observations. That is, in fact, the foundation of science--it must be consistent with real-world observation.

There's no point in continuing until that issue has been resolved.

If you have changed your position and are now agreeing that the muzzle gases can travel faster than the speed of sound in air, much faster, in fact, than the bullet, and can catch and affect the bullet as the source I provided proves, then please clearly say so and stop arguing the point. Also, if you really are motivated by a desire to provide knowledge and understanding, you will certainly want to explain what it was that led you to make such an elementary error and how you misinterpreted the plethora of supporting data you provided to support the incorrect claim.

 

[davidsog]

You absolutely claimed several times that the muzzle gases could not travel faster than the speed of sound.

John, in many ways we have much in common in this discussion. I had very good professors and attended one of the top 5 engineering schools for this discipline. Fortunately, those professors were able to explain this barney level to a glorified grunt.

It might help for you to understand how supersonic air enters and exits a tube.

Again, this will also highlight the importance of a good properly formed crown in a barrel.

That normal shock is of course reversed as our flow of our expanding gases exit the barrel. That is not important. What is important is the fact that normal shock is right at the exit and completely covers the exit of the barrel. That normal shock would exist with and without a bullet in the way and it just formed by the nature of the gas movement encountering the air mass(atmosphere).

In an jet engine we have what is called a variable exhaust nozzle. Think of it like a crown of a barrel that can change shape including to an improperly formed crown. That is how your get your mach diamonds you were focusing on but please forget those...it won't help you understand what is going with a bullet because our barrels have proper crowns without variable exhaust nozzles. This property is also why supersonic aircraft can have air breathing turbine engines.

The shape of the crown forms expansion waves conserving energy as the flow can provide it. Those expansion waves will not cross a normal shock to influence anything upstream. Those expansion waves at the crown will increase the velocity of the airflow until the run out of energy and without mass flow that takes very little time. When the bullet exits, it is forming its own Normal Shock. It forms a normal shock immediate upon contact with the air mass both at the bow and at the rear of the bullet when it reaches the air mass.

That Normal Shock formation at the muzzle exit send that energy out as a vibration that creates that ball of normal shock expanding at the muzzle.

Two questions you must have the correct answer too in order to understand what is going on.

1. What is the velocity of the air at the normal shock?

2. What is the velocity of the air immediately downstream of and behind the Normal Shock?

 

[JohnKSa]

So, are we back to you saying that they can't exit at supersonic speeds again? Just trying to keep things straight.

Fortunately, those professors were able to explain this barney level to a glorified grunt.

I would argue that they, in fact, did not, given that your understanding of the situation obviously contradicts real world observations. Muzzle gases do exit at substantially higher than the speed of sound in air and continue at supersonic speeds for some non-negligible distance after exit.

What I think is going on is that you understand a specific case very well and assume that it is more universal than it is. So you are taking correct principles from one case to another case where they do not apply--which is resulting in nonsensical claims and assertions.

I provided a source that proves how muzzle gases behave and you have studiously ignored it since I posted the link.

https://www.mdpi.com/2226-4310/11/5/381#:~:text=Because the velocity of the,was formed at its bottom

...the high-temperature and high-pressure gas jet expanded at a much higher rate than the velocity of the moving body. It expanded more quickly under the influence of the initial jet. The muzzle jet encountered the moving body...​

"The high-temperature and high-pressure gas was sprayed behind the moving body, rapidly expanded at a speed above 1900 m/s, and chased and impacted the body to form shock waves at its bottom and on both sides of it."​

 

[davidsog]

I provided a source that proves how muzzle gases behave and you have studiously ignored it since I posted the link.

There is nothing in that report that refutes a single thing I have said nor is there anything that says muzzle gases have any effect on a bullet.

It actually relates what I just told you in my last post.

The muzzle jet continuously sprayed out gas, and the forward-moving shock wave collided with the reflected shock wave to suppress its development.

The shock wave of the muzzle jet under interference by the initial jet was complex and featured shock–shock collisions and shock–vortex collisions in the flow field that suppressed the expansion of the muzzle jet and led to the formation of multiple reflected shock waves and high-pressure zones.

You can clearly see that in the photos.

In fact, it concludes exactly what I said in my first post on this subject:

Owing to the low energy of the initial jet—one order of magnitude lower than the energy of the muzzle jet—the force of its impact on the high-speed moving body was relatively small, while the impact on its lifting force was relatively large but could be ignored.

You understand that the largest component of energy delivered to the bullet CAN BE IGNORED......

It is not enough energy to overcome the bullets energy to cause a positional shift..........

Not surprising at all given that it must cross a normal shock.....which is a violation of the laws of nature.

davidsog says:

Knowing what I know of Aerodynamics as a someone formally educated in Aeronautical Sciences my first instinct is that the gases escaping from the barrel do not influence the flight significantly in MOST cases provided everything is in proper working order for the rifle and ammunition.

https://thefiringline.com/forums/showpost.php?p=6977638&postcount=398

I am banging my head against a wall here and making my pistol rusty from sticking it my mouth.

If you correctly answer those questions at the bottom of my last post, you will go a long way towards figuring this out for yourself.

 

[davidsog]

The muzzle jet encountered the moving body...

The rest of that sentence is important:

The muzzle jet encountered the moving body such that this suppressed its development and led to a reflection in the shock wave and a change in its direction of propagation.

There is a shock wave collision between the Normal Shock of the bullet and the Normals Shock formed by the gas exiting the tube.

That collsion changes the direction of the shock wave propagation. It does not change the direction or flight of bullet.


Understand??? The shock collision suppresses the exiting muzzle jet.

 

[JohnKSa]

There is nothing in that report that refutes a single thing I have said...

That's obviously not true.

You've said that the gases are moving slower than the bullet after exit. The report absolutely contradicts that.

You've said that the gases are not exceeding the speed of sound in air. The report absolutely contradicts that.

I am banging my head against a wall here and making my pistol rusty from sticking it my mouth.

I can see that it must be extremely frustrating for you. It is obvious that you have made claims that are incorrect and unsupportable and yet you can not seem to bring yourself to admit it, even in the face of absolute proof that you are wrong.

So, are you still claiming that the muzzle gases are subsonic and that the bullet is moving much faster?

 

[davidsog]

You've said that the gases are moving slower than the bullet after exit.

John

What is the velocity of the air immediately downstream of and behind the Normal Shock?

The answer is in the Middle column there, under Normal Shock.

Cross reference it with "Effect of Velocity and Mach Number"

I highlighted it for you so it would be easier to find.

It says something about SUBSONIC. Is your bullet traveling at a subsonic speed?

 

[JohnKSa]

This is really, REALLY simple. Are you saying that these two statements from the paper are wrong?

"...the high-temperature and high-pressure gas jet expanded at a much higher rate than the velocity of the moving body..."

"The high-temperature and high-pressure gas was sprayed behind the moving body, rapidly expanded at a speed above 1900 m/s, and chased and impacted the body to form shock waves at its bottom and on both sides of it."

Unless these two statements are both wrong, your statements about the velocity of the muzzle gases can not be correct.

 

[davidsog]

So, are you still claiming that the muzzle gases are subsonic and that the bullet is moving much faster?

Yes. Just like your report says it does....

 

[davidsog]

"...the high-temperature and high-pressure gas jet expanded at a much higher rate than the velocity of the moving body..."

John,

Expansion waves will increase the velocity and increase the velocity to supersonic. Expansion waves are not normal shock wave. Very different animals. So when I said multiple post's back that expansion waves form....
It means the velocity increases.

You are very much misunderstanding and confusing when the report is talking about airflow behavior of the muzzle jet that has NOTHING to do with effects on the bullet.

Different subjects.

The FACT Normal Shock forms at the front and rear of the bullet isolates the bullet.

The FACT normal shock forms at the muzzle due the exit gases encountering the atmosphere means the air is subsonic at the muzzle.

Expansion waves will form on the crown and the report is saying the collision of those normal shocks changes the direction of propagation of the wave. There is not enough energy from the exit gases to effect the bullet.

That is what your report says.....

 

[JohnKSa]

You understand that the largest component of energy delivered to the bullet CAN BE IGNORED......

I understand that you didn't read that report very carefully.

"Owing to the low energy of the initial jet—one order of magnitude lower than the energy of the muzzle jet—the force of its impact on the high-speed moving body was relatively small, while the impact on its lifting force was relatively large but could be ignored."

"The moving body accelerates and compresses the air in front of it under the propulsion of gunpowder gas in the tube to form the initial jet."

The initial jet is the gas in front of the bullet, which is quite different from the gas jet/muzzle jet that follows the bullet out of the muzzle.

Just like your report says it does....

Well, it's clear that this is pointless. When the paper very obviously and repeatedly says X and you claim it doesn't that sort of limits the possibility of constructive exchange.

Is it that you don't believe that 1900m/s is faster than the speed of sound? It is. It's over 5x the speed of sound.

Or is it that you do not understand what "chased and impacted" means? That can't happen if, as you claim "the bullet is traveling much faster than" the gas jet.

 

[davidsog]

The initial jet is the gas in front of the bullet, which is quite different from the gas jet/muzzle jet that follows the bullet out of the muzzle.

The point is the shock wave collisions John.

And what is the speed of the Normal Shock formed at the bow of the bullet in the initial jet....

What is the speed of the Normal Shock formed at the muzzle?

What is the speed of the Normal Shock formed at the end of the bullet



Mmmmmmm

5. Conclusions
In this study, we examined the characteristics of development of shock waves and vortices in a muzzle jet in case of interference by the initial jet for a launch device with a large diameter and a long barrel with a high kinetic energy of the muzzle. The conclusions are as follows:
(1)
The shock wave of the muzzle jet under interference by the initial jet was complex and featured shock–shock collisions and shock–vortex collisions in the flow field that suppressed the expansion of the muzzle jet and led to the formation of multiple reflected shock waves and high-pressure zones. The strong shock wave of the muzzle jet collided with the weak vortex of the initial jet, causing it to disappear and leading to the formation of a stable vortex of the muzzle jet in the flow field. The muzzle jet without interference by the initial jet had a clear and simple structure.

Well, conclusion number one says NOTHING about the bullet. It speaks only of the flow field.

Is it that you don't believe that 1900m/s is faster than the speed of sound? It is. It's over 5x the speed of sound.

Or is it that you do not understand what "chased and impacted" means? That can't happen if, as you claim "the bullet is traveling much faster than" the gas jet.

You are confusing case 2, a simplified model to clarify the flow field....with reality.

Figure 14 shows changes in the pressure (0.5 ms~10.0 ms) in Case 2 (the model without interference by the initial jet) on the plane of symmetry over time. Due to the absence of interference by the initial jet, the structure of the muzzle jet was more regular than that in Case 1. The body moved forward at a high speed to form a CS at the front. The high-temperature and high-pressure gas was sprayed behind the moving body, rapidly expanded at a speed above 1900 m/s, and chased and impacted the body to form shock waves at its bottom and on both sides of it.

Case 1 involved the complete structure shown in Figure 1a. It featured a moving body, a 30 m long tube, and the domain around the muzzle. Case 2 ignored the motion of the body inside the tube, as shown in Figure 1b, and considered only its motion outside the muzzle. Case 3 ignored the moving body altogether, as shown in Figure 1c, and involved only the initial jet and the muzzle jet. In Case 4, the motion of the body inside and outside the bore was ignored, as shown in Figure 1d, and only the domain outside the muzzle was considered.

The report is very clear on its conclusions. If your conclusions are different, then they are probably not correct, John.

 

[JohnKSa]

You are confusing case 2, a simplified model to clarify the flow field....with reality.

You still haven't read the report. It contains data collected from an actual firing. Figure ten shows: "Development of the supersonic muzzle jet over time."

Also from that section:

"...the velocity of the gas ejected from the muzzle exceeded that of the moving body..."

" the high-temperature and high-pressure gunpowder gas inside the tube was quickly sprayed out to chase and surround the moving body."

"Therefore, the method of simulation used in this paper could accurately simulate the characteristics of the muzzle jet of the models."

Well, isn't that interesting. The real world experiment showed that the gas jet moves faster than the bullet. It chases and surrounds the bullet. And it showed that their models were accurate.

Well, conclusion number one says NOTHING about the bullet.

Just out of curiosity, did you even bother read the first sentence of the Introduction? You know, the reason that the research was done in the first place?

I'll quote it now, just for fun.

"When a barrel weapon launches a projectile, the muzzle flow field will cause initial disturbance to the projectile’s flight, reducing its shooting accuracy and increasing its impact point dispersion."​

The report is very clear...

Indeed it is.

The point is the shock wave collisions John.

Actually, the specific point is the quote you took from the report does not say what you claimed it does. You didn't read (or didn't understand) that the initial jet is not the gas jet/muzzle jet. The gas jet/muzzle jet is an order of magnitude more energetic than the initial jet.

The more general point is that you are mining the report for things that you believe support your point of view and both making errors in that determination based on carelessness or lack of understanding and apparently ignoring anything that contradicts you, however clear that contradiction is. Another example of a rather disturbing pattern of behavior.

Worse yet, even when faced with the incontrovertible truth that you screwed up (i.e. confusing the initial jet with the muzzle jet/gas jet and using that as the basis to try to make a point) you still can't bring yourself to admit that you made an error.

This all highlights the total uselessness of this exchange.

• You post things and then feel free to contradict them later, even when faced with your original posts.
• You post supporting material and then contradict it, presumably because you don't understand it.
• You accept sources as valid but then blatantly contradict the contents.
• You quote material from sources that you accept as valid but then make it clear by your comments about the material that you didn't understand it.
• It appears that you are unable to admit it when you make an error.

The combination of all those, especially the last point, means that it's impossible to have a constructive exchange and pointless to try. And I think I've had enough pointless to last me for awhile.