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

I actually think the term "cylinder choke" is not only an oxymoron but it is confusing to many. Cylinder is just a way of saying that there is no constriction at all. Except in the case of jug choking, which is a stand alone situation.

SRH

yes, I know that and can repeat it, but as a dumb professor, I want to understand the mechanics of WHY constriction, not final diameter matters. I feel this missing mechanism is probably somewhat embedded with the arguments above that I have, admittedly, only skimmed through. There is a difference between knowing and understanding. I'm looking for the latter.

I'm sorry, Brent, but I don't understand exactly what's missing, or what to clarify to help you understand it.

Maybe this .......... final (inside) diameter matters greatly, but only insomuch as it can provide the difference from bore diameter that is needed.

Keep asking. We'll get to the heart of it eventually.

SRH

Reeely? Do you have any notion of physics whatsoever? Just what sort of professor are you? Physical sciences and logic seem not to be intrinsic to whatever it is. Not to be mean-spirited or anything but you have to make some effort to understand some basic concepts or just be what looks like a troll. I mean, your statements are inane but wonderfully clever.

just sayin'

Let's ignore that nasty forcing cone thing used to transition pellets from shell in the chamber to bore.

1 1/8 oz. shot in a 10g (.775") - 12g (.729") - 14g (.693") MLs without choke constriction will yield essentially the same pattern.
1 1/8 oz. shot in a 10 - 14g MLs, each with the same .030" choke constriction (bore ID minus muzzle ID) will yield essentially the same pattern.
Too narrow a bore (and I don't know what that would be) causes elongation of the shot column = more pellets in contact with the barrel = more deformation = deterioration of the downrange pattern. Or maybe not with steel shot.
Too big a bore (and I don't know what that would be), unless the appropriately oversized wad was used, would be associated with gas 'blow by' which disrupts shot charge on exiting the bore = deterioration of downrange pattern.

More from Compton

p. 123 Effect of choke (.000� - .050�) on lateral pattern spread at 40 yds.

p. 128 It was found that for the same (choke) constriction the 1" parallel section produced a slightly tighter distribution of pellets at 40 yards than the linear taper profile for every batch of ammunition tested. However, the standard errors associated with the distribution show that statistically there is no significant difference between the two profiles, expect for the one steel load tested where an improvement is seen when using the 1" parallel section profile.

Now this is strange!
p. 129 The other variable which can be altered in the test barrel to change the internal ballistics is the chamber length. In Table 3.10 the standard deviation and pellet counts at 40 yards are given for a 36g load of #4 lead shot loaded into a 2 3/4� cartridge cases which were fired through a selection of chambers lengths. The averaged results show a definite alteration to the lateral dispersion of the shot cloud large when using the wrong chamber length. The tighter pattern generated by 2 1/2� chamber length may be caused by the restrictive crimp opening acting like an internal choke.

Altering the chamber length changed the lateral dispersion of pellets and increasing the constriction of linear tapered profile chokes over 0.030" has little effect on the lateral pellet distribution. These findings reinforce the attitude that many aspects of shotgun ballistics, especially patterns, have no satisfactory theory to predict or explain the effects of the internal ballistics of a gun on the downrange behaviour of a shot cloud.

Well that 'splains everything

Dr Wanker actually got it pretty much right with his 3 dimensional balls on a pool table analogy... even if that explanation was a bit of an over-simplification.

There are interactions as those little balls, or pellets move down a parallel bore that result in what we call a cylinder bore pattern. The relatively abrupt change when the little balls hit the tapered section we call choke obviously causes the paths of the little balls to become influenced into a tighter pattern as the constriction become greater, within limits. But we also have to factor in a lot of other variables such as the velocity of the little balls, their hardness, roundness, and mass. Then there are still other variables such as shot cup material and thickness, polish of the bore, gas blow-by, number of pellets, i.e., number of collisions, etc. that will introduce pattern variations from using differing loads in the exact same barrel.

Because of the large number of subtle variations, and the unknowns concerning their final influence upon the resulting pattern, I suspect it would still be very difficult to create a computer program that could predict a shotgun pattern with a high degree of precision. It is simple physics. Kind of like understanding and explaining the expansion of the universe, but on a somewhat smaller scale.

Just think, we all may be on our way to God's pattern board!

p. 155 �Three-Dimensional Representation�

The general shape of the shot cloud revealed that the pellets arriving first (leading edge) are located in the centre of the pattern, and the trailing edge pellets appear at the outer regions. The deformed pellets, collected at the outer parts of the pattern, travel at the trailing edge shot cloud. The well formed pellets, associated with the pattern centre, are to be found at the leading edge of the shot cloud. With the greater associated deformation on pellets at the rear of the load, caused by the pressure in the barrel compressing them into the pellets above, a similar relationship between the pellets deformation and location in the shot cloud is seen in both experiments.

SUMMARY

p. 160 The longitudinal distribution of pellets in the shot cloud at ranges between 20-50m was shown, via shot cloud length, to be unaffected when the internal ballistics of the gun, such as choke, were altered. However, from high speed photography it is known that the initial distribution of pellets is affected by the internal ballistics. Therefore it is assumed that the in-flight effects of the pellet become the more dominant factor, thus masking the internal ballistics effect, at ranges greater than 20m.
From the analysis of the shot cloud profiles it was established that the longitudinal pellet distribution is best described as a Rayleigh distribution.

Analysing the lateral distribution of pellets in the shot cloud it was established that there are two independent distributions, that is the horizontal (x) and vertical (y) pellet distributions. These two distributions were shown to be best described as Gaussian (�bell curve�) distributions.

Lateral pellet distribution did not reduce, after 0.030". These results were obtained using a linear tapered choke profile and further experiments are required on different choke profiles to verify this relationship between lateral distribution and choke constriction.

It has emerged clearly from this work that it is not possible to produce a satisfactory theory which can predict the downrange behaviour of shot clouds from the muzzle condition in sufficient detail. Further work is required to understand the full effects of choke constriction and choke profile on shot clouds.

It was shown that the launch effects were the major influence on the shot cloud width and the in-flight effects were more dominant in the shot cloud length masking the possible launch effects over the measurement ranges.

"Analysing the lateral distribution of pellets in the shot cloud it was established that there are two independent distributions, that is the horizontal (x) and vertical (y) pellet distributions."

No kidding.

Choke effect does one thing that we can easily observe.

It introduces a velocity differential. The leading pellets are started on their way 50 fps. faster (or so) than the trailing ones.

This introduces a time of flight difference that is increased by aero effects on the deformed pellets.

So, vertical dispersion must take place due to time of flight differences.

This part, however cannot be true:

'The tighter pattern generated by 2 1/2� chamber length may be caused by the restrictive crimp opening acting like an internal choke.'

The shot mass is under heavy and continuous acceleration right to the muzzle. Whatever speed differential is introduced by the chamber cone must shortly disappear. The shot mass enters the choke as a cylinder.

I'm the kind of professor that would be quite happy to see you explain this in partial differential equations if you would. I can handle the physics just fine too, but you have yet to say anything that is helpful at explaining the differences between the two hypothetical bores. I take it from your tone, you either cannot do it or, at least, are not interested. Just say so. I can find something else to do with my time that will save you the trouble of the insults.