But someone said this was all about fluid dynamics. Okay, let's talk fluid dynamics. Frankly I don't see that being any better than an approximate analogy. But I'm listening, or I was anyway.
If the pictures on page 3 of this thread do not convince you that the shot charge fired from a choked barrel lengthens between 6 feet and 14 feet then nothing will. The only possible thing that could cause this is speed differential. The trailing pellets are going slower than the leading ones in spite of the drag front acting on the leading pellets. The trailing pellets must have been launched at lower velocity.
Yup, I got that. Got that many decades ago, actually. Doesn't do a darn thing to answer my question either.
[quote]If there were an endless constant stream of pellets traveling through the choke, they would all behave the same at exit. This is clearly not the case in the physical shotgun.
The 18 foot photo shows the pellets starting to bunch up and spread due to the same effects that work on the cylinder choke shot mass. That's 6 yards downrange and still only 1/3 the diameter of the cylinder choke sample.
That is 'choke effect' plain and simple and that's all there is to it.
This is a description of the phenomenon, not an explanation or understanding of it.
It's caused by a differential in speed between the leading and trailing pellets. If all the pellets shown in the 6 foot picture of the choked barrel were going the same speed, the pattern would already have started to mushroom like the photo above it.
And yet all the pellets traveled through the same choke.
Well, that certainly DOES bear some resemblance to a de Laval nozzle, doesn't it?
Thanks but I'll retreat to other environs. I'm not finding what I was looking for.
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
