Musket Ball.

Pellets have friends. Think of them as kind of a Nascar field.

 

Could you add a dimple or a flat spot to that and see their effects on the flight? very neat stuff

 

Pretty colors!

 

Doc - invent some pellet shape that flows through the air better so we don't have to push it so hard to start with. Less recoil, more effective force downrange. Is that what you're after? Why, Doc, why? Just asking, not criticising.

Joe

 

excellent thread. however pellets are not perfectly round. I think of them as a knuckleball. oz

 

Good information. In your research have you found the evidence to prove or disprove the theory that mixing shot sizes gives you an inconsistent pattern? If you could disprove that theory, many of the posters on TS.com could mix their 7 1/2s and 8s in their loads and would quit asking which size to use. LOL Just kidding as it will never happen. IMHO If you post it they will come. Omaha

 

Dr. Jones, computational fluid dynamics is a discipline that has been around for quite some time, not a commercial program...LOL!!! I'm sure that you are referring to a software program, though.

Since you have this tool at your fingertips, what would be extremely interesting is if you could model two types of shot pellet; one that is coated with graphite -vs- one that is uncoated. This would provide some useful information for all of us. Do you have the time and inclination to do that and post the results? It would be much appreciated.

 

Great illustrations and I want to make things much more complicated. We are primarily interested in what is going on in a cloud of shot. Trying to visualize many shot interacting is beyond my abilities.

Pat Ireland

 

First, let me point out that getting the models to the current state has taken about 6-12 months on and off. Although it looks like "just one measly sphere" the model takes about three days to run on a workstation.

In some respects the model is quite limited. All it does is work out the average flow, turbulence levels, temperatures etc. In reality, the turbulence is constantly changing with eddies constantly being shed from the back of the sphere. Modeling this is 1000s of times more numerically intensive. It might even be impossible.

To see why this is important, take a quick look at the link above about the aerodynamics of paintballs. Just read the headings in blue and you will appreciate just how complicated this apparently simple subject can be.

However, in its current state the model gives drag figures that are consistent with Shotshell Ballistics for Windows (about 20%) which was my first objective.

In response to the questions:

skeet2day - 7.5 vs 8s? It should be obvious that altering the size of the sphere by a small amount will not make a profound difference. All that will happen is the overall effect of deceleration will alter slightly. This is a combination of frontal area, pellet mass, and how the drag coefficient changes with pellet size (basically how the air flows over and breaks away from the pellet). It is easy albeit time consuming to rerun the model with a smaller pellet. But we know from experience of downrange velocities that the difference between 8s and 7.5s is small.

JBrooks, omaha, Pat - broadly effects of pellets interacting: Look at the top picture. The pellet is 2.4mm across (0.095-inches). The extent of the disruption of the air flow is ~3-pellets widths out the side, 2 to the front and 5 to the rear. Once pellets are further apart than this they are effectively independent. There isn't any interaction.

recurvy - pellet coating: Probably no effect. The CFD code assumes a stationary boundary layer of gas on the object surface. At a molecular level this is meant to represent the molecules that stick to the surface. I know what you are thinking now, "but what if these molecules could slip better rather than stick". It will not make any difference. The coefficient of friction of air is much less that Teflon anyway.

*** I just had a thought though: Since the air is getting pretty compressed does its effective viscosity increase? I don't know. Maybe someone knows if supersonic planes / missiles get a coating of something.

*** Whatever, the CFD code cannot model this effect.


Rifleguy, oz - broadly misshaped pellets: I have a model of a pellet with a flat on it. Let me just say that things "get interesting". The problem with "interesting" is whether or not it is correct. Normally when you use CFD code you have some real tests to correlate with. I haven't got this luxury so when I get an odd result that still delivers plausible results I need to be very cautious before making my Eureka shout and running down the street in my birthday suit. I am also very aware of how little the CFD code is modeling. See the paintball link above and this link:

http://www.iihr.uiowa.edu/projects/low_reynolds/

with this pic at the bottom:

flicher - effect of velocity: Probably none. Again if you look at the first pics, what can happen if the velocity changes a bit? The drag goes up or down but not much changes. The pics above are for Mach 0.9. I have done Mach 1.5 as well. The pressure, temperature, velocity profiles get greater and more defined, the overall deceleration increases but there's no catastrophic change. Of course there is a possibility of some effect not modeled coming into play (see the paint ball link again). My practical advice would be to drive pellets as fast as possible so you can use smaller pellets all subject to recoil not putting you off. Unfortunately your trap rules stop you going down this route.

Joe - a better pellet shape? That'll be a bullet then. Incidentally, a bullet complete with rifling marks is easier to model than a pellet.

Andrew.

 

"I need to be very cautious before making my Eureka shout and running down the street in my birthday suit"......LOL!!!! That was funny.

Thanks for the very interesting post. It's quite fascinating.

 

Thanks. That was really interesting and very nice of you to post it here for everyone to see.

Hauxfan!

 

Andrew,

When the pellets pass through the sound barrier I believe they encounter turbulence which disrupts the pattern of the pellets. Am I right or wrong about this concept? HMB

 

HMB, Depends what you mean by turbulence. There is turbulence all the time. The wake behind the pellet is turbulent, the air being pushed around is turbulent. The pellet is having a pretty buffeting time whatever speed it is traveling at. I'm not sure what effects supersonic has on a tiny round sphere. When I run the model at Mach 1.5 I get higher and more defined pressure and velocity contours. This is a trait of so called supersonic effects. What I don't get is the huge pressure waves you see on aircraft. It could be because the model is wrong (CFD models tend to be diffusive. This means they tend to smear sharp effects) or simply down to scale. A plane is of course millions of times larger than a pellet. Maybe if I ran the pellet at Mach 1000000 I would get the shock wave. Even a bullet is ~150 times+ heavier than a pellet so when traveling at Mach 1.5 it is having to move a lot more air.

Bear in mind that a pellet is not at all like a bullet. A bullet flies at a slight angle (due to spin and drag) and has rifling interacting with the air. As the shock wave moves up/down/around the bullet it will have different effects and may nudge the bullet one way or another that affects its trajectory thereafter. With a single bullet your are wanting the absolute best repeatability with every projectile.

A pellet and a pattern are quite different. The pellet is pretty much symmetric. As the pressure waves move around the pellet they do so equally so there is no effect to push the pellet off course. Even if there was an effect, all it does is add to the randomness of the pattern. Random is random so a little bit more mixing up doesn't make any difference. The only downside is that the additional mixing will (on average) increase the pattern spread. How much? Probably tiny but that's a guess part supported by the fact that patterns are not affected by other things very much.

Andrew.

 

Doc - Hope you saw the video of the tank shooting ball bearings. The dynamics was pretty interesting with some pellets moving away from the center, some falling back and away, and other scenarios. Overall the shot cloud changes shape pretty dramatically. It would be neet to draw the circumference of the cloud and see it change as everything moves down range. And then you've got a 3D version to think about.

Good to hear from you.

Joe

 

^

 

I sure hope that Neil doesn't get wind of this thread. He'll be on you like a numerator on a denominator.

Tron

 

Joe K, It's a little known fact that before the best tank commanders take delivery of their barrels they send them off to a well known barrel guru for "tweaking". If you look closely at the tank video you'll see the results . . . .

Andrew.

 

Dear Dr. Jones,

Wow - I appreciate the work...

I know this is asking a lot, but have you thought of extrapolating this for a shot stream, or even for a wad filled with shot?

I do appreciate the work you've put into in this so far, but the next logical question would ask how this impacts upon a group of pellets traveling together in a shot stream (both generally for the stream and on the interaction of the individual pellets), and how this impacts upon patterns, wad choice, etc.

I guess you could even apply it to choke selection/design as well.

Food for thought, and thanks again for sharing this.

David D

 

Doc

What program did you use for the CFD work. I am a senior engineering student and this stuff is awesome to me. In my fluids class we didn't get to do a lot with CFD and wish we had done more. Great simulations I have worked some with loading simulations with gears and such I know how long coming up with these numbers take. So nice work the results are fascinating.

-Clem

 

Clem, The top pics are from CD-Adapco's CCM+. It has very powerful post processing capability, almost as good as specialist packages like Ensight. It also has a fanatastically flexible and powerful mesher. I have also used Star 3.xx and Fluent. I guess the maths of the solvers is all pretty similar but CCM+ is much more easy to use. For me the most powerful thing is that its macro langauge is pure Java and since I can programme in Java I can do some pretty whizzy things in CCM+ like include my own applications as pop-ups! In theory I could run Shotgun-Insight inside a CFD simulation. I can't think of a use for that but it shows the flexibility if CCM+.

With luck this animation will embed (you need to click play for it to run):

http://www.cd-adapco.com/media/videos/6dof/duck.swf


<embed loop='True' src='http://www.cd-adapco.com/media/videos/6dof/duck.swf'>
</embed>


David, I'll state again one of the implications of the first picture: Pellets are pretty much independent once they are giving a recognisable pattern. To "calculate" how the pattern develops is "simply" a case of understanding how an individual pellet behaves and then applying a random model to show what happens on average to an ensemble.

When they are still interacting with one another (just after the muzzle) needs some thought. I don't know if a coarse mesh will suffice just to show how pellets move apart. I guess not, since what we really want is an accurate model to know what and why things happen. We know pellets spread so just showing "spread +/- 50%" doesn't really move things forward. Using the detailed mesh with the moving effects like the duck above is beyond my computer power.

When shot are in the muzzle I do not believe they behave like a fluid (at least not any useful that would allow choke tuning analyses), hence the CFD tool cannot help.

Andrew.

 

Doc - you are right about the affect of a coating - none. But as far as a pellet cloud, I htink you are overlookigj something. You are assuming that each pellet in a cloud pushes through clean air. Not the case. If it were, patterns would be super tight all the time (assuming round pellets) as there would be no turbulence, eddie effects, etc. to help scatter them.

Joe

 

Joe, Read the link about the paint balls above re the heading "Vortex induced forces". This suggests that even in perfectly still air with a perfect sphere you still get the ball pulled off line. That's what the second animation above shows.

I can't model that affect to I am limited to what I can model.

I can model mishaped pellets and these definitely have forces that pull them off line even if the air is still.

So, assuming still air does not lead to super tight patterns.

I think I am of the view (but reserve the right to change it) that eddies and other things in the air do not have much affect on patterns. The decelerative force on the pellet due to its forward motion dwarfs everything else. How these forces interact with pellet imperfectiions will (I think) also dwarf most other effects . . .

. . . . but I could be wrong.

Andrew.

 

Dr. Andrew- Fascinating information. My understanding of fluid dynamics is at the very best, minimal. I am in agreement with you that shot irregularities (few would be perfect spheres) would play a greater role in patterns than the interactions of perfect spherical shot.

I can not explain why I find your models so intriguing. I have looked at them in detail for well over an hour. You are interfering with my work productivity, but you made yesterday very enjoyable for me. Thank you.

Pat Ireland

 

Andrew, I too find your work fascinating and thank you for sharing!

It doesn't surprise me a lick that my friend, Pat Ireland, is also fascinated. I once saw him look at a missed clay for a good 10 seconds in an attempt to figure out how that bird could fly off with his heart shot out! Hap

 

Holy ####. If our ancestors knew how complex the flight of spheres actually is, they wouldn't have bothered to develop the musket. This stuff is very neat, and potentially useful for trying to conceptualize shot pellet patterns. From the work Dr. Jones presents, it seems that once the pellets are separated by 3-4 pellet diameters, the flight of each sphere is independent of the rest of the pack. However, we also know that the front spheres separate from the pack prior to rear pellet separation. So, it appears that a mental model might consist of a clump of spheres that decelerates at a lower rate than the individual particles that make up the clump. The individual particles must be shed radially, as the main body proceeds, and once an individual particle is 2-3 diameters away from the pack, it assumes its solo ballistic flight path. This model also provides some insight into how the length to diameter ratio of a particular load affects the shot pattern. It gives me some clues on how to proceed with my high speed photography. Possibly, some high speed Schlieren photographs are in order. Tom S. (welderman)