doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Shot Distribution in Pattern

As soon as I figure out what is not working wright on my computer!

DDS

I am the guilty party for saying choke is largely about fluid dynamics. I remain guilty. The larger the number of discrete particles (atoms, molecules, ....., shot pellets, gravel, rocks) in the flow field, the more exacting the predictions. 500 pellets is a very small number of particles. Yet, we have a flow field, a constriction, and a narrower, more cohesive flow. Where am I wrong?

I am providing an explanation of the phenomenon. As the leading edge of the shot column enters the choke, these leading pellets accelerate/speed up to get out of the way of the pellets behind them. They accelerate all the way through the choke, as do all of the pellets, gaining some 50 fps. The leading pellets have experienced higher velocity for some fraction of a second longer than the trailing shot. Therefore, they are farther ahead; ergo the shot column is lengthened.

Yes, all the pellets traveled through the same choke, but not at the same time. Therefore, the lead pellets are farther ahead than in the unchoked column.

The WS-1 choke profile does look like a de Laval nozzle in that it has a convergent and divergent section. Since we don't know the speed of sound within the shot column (This is entirely different than the speed of sound in the surrounding air), we are unable to calculate parameters for the nozzle and have to rely on experimentation. I am unaware of any experiments to incorporate a divergent section in a full choke nozzle.

One more time. What are you looking for that has not been answered?

DDA

A nozzle does not need a divergent section unless the intent is to accelerate the flow mass beyond its sonic velocity. Well, the interaction of forces and moments on discrete particles pretty well explains all statics and dynamics. Unfortunately, that foundation gives us no information relevant to individual situations. Exactly which forces and moments are acting within the choke?

"May the force and moment be with you!"

DDA

Do the shot pellets have to retain a spherical shape for the flow theory to hold up? For example, steel shot that may be less subject to shape distortion seems to flow through a shotgun choke in a different way than lead does. If the shot, or some of the shot, can be shown to become distorted, is their flight through air and disrupted air predictable enough to stay within the theory? Only asking, no other implications.

No, any shape will do. However, it seems likely that there would be some shape factor. How do you see steel and lead shot differing in response to choke constriction? Distorted shot has been shown to produce a higher % of "fliers" than spherical. That said, I think turbulent air behind the lead pellets is not very disruptive of the shot's flight path. A pellet getting a sideways boost in one direction is just as likely to get a similar boost in the opposite direction a little farther along. Prediction of flight path of projectiles through still and turbulent air is fairly settled science. Note that choke effect ends at the muzzle. From that point on, the flight path is set by muzzle exit forward velocity, sideways velocity, and aerodynamic effects encountered along the flight path.

That help?

DDA

So, if the pellets need to speed up to get out of the way of the following pellets when there are no more following pellets that need would disappear.

The last portion, say the length of the conical section or even close to the diameter of the bore, could as easily fill the space behind with the effect that a considerable fraction of the payload does not accelerate at all or even is slowed. Given the force needed to displace the pellets ahead vs the pressure required to resist the wad, this seems quite plausible. We are still accelerating about 20 feet per second per inch here, so inertia is not on the side of going faster.

There is also the conservation of energy bugaboo. An extra 50 fps for the entire shot charge seems unreasonable. This energy has to be extracted from the expanding gas, at a rate of V squared.

I can't reconcile the observed length of the full choke shot charge with equal acceleration of all pellets through the choke.

The last layer of pellets would probably ride the wad out the muzzle. But, the front layer has had higher velocity for a small fraction of a second. Whether or not the last layer of pellets has full acceleration from the choke, the shot string will be stretched out due to the front layer having longer at higher velocity. I don't think anything slows down. The acceleration of the pellets is provided by a drop in pressure internal to the shot column. I know that is counter-intuitive, but it is true.

Does that help? More questions or observations?

DDA

Thanks much DDA. Purely on the two dimensional result of a pattern plate, I believe steel shot can deliver a similar pellet count, if all else is equal, with less choke constriction.

When I see pictures of long shot strings, it might appear that the effect of turbulence would be increasingly difficult to calculate due to the random and overlapping distribution of the shot creating it. I've also wondered if trailers were to some degree flyers, distorted shot subject to increased drag, and not only the tail end of a flow model. Anyway, only thoughts.

What could be easier? Take a good look at Newton's Laws of Motion. Nothing complicated there and readily understandable. Then re-read my comments in this thread. Newton's Laws of Motion applied to the mechanical interaction of solid interacting bodies subject to external and resultant inter-body forces just like Newton describes.
TabA/SlotB I mean, this is REALLY simple. A body at rest/in motion remains at rest/in motion until etc etc etc

HTH

I can only assume that you are joking that the forces involved are not obvious. Seriously. Are you truly incapable pf visualizing that?