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

I will not argue the point that "Central Thickening" is a misnomer. However it has been in use for so long I think everyone understands the term.

Unfortunately it gives a wrong impression of how patterns are distributed. There has been so much incorrect information based on limited, non-statistically supported data that we can ill afford to continue to have inaccurate discussion. In my opinion, there has never been truly accurate data pre Jones. Gun writers of the past get a pass from me due to lack of solid data.


No problem with accepting that all patterns/groups follow a similar type of dispersion.


This statement is going to take a bit more explaining to an old hillbilly. I simply find it unbelievable that load with a 10.5:1 ratio would ever be identical to one having a 2:1 ratio at any at range.

Hillbilly you may be, Miller, but you are a very smart one. Chokes function is to stretch out the trumpet. Think of open choke as a coronet and full choke as one of those long ceremonial trumpets. If we look at the pattern where the trumpet diameters are the same, we will find statistically identical patterns. Think carefully. Full choke patterns at 40-45 yards perform more or less identically to IC at 25-30 yards. Same performance implies same pattern distribution.

Other factors also have an effect on the pattern, a major one being the choke.

Choke is the major influence as to how quickly the pattern blooms. Note that bloom and wither do not change the distribution. It is a Rayleigh out the muzzle and a Rayleigh when it hits the ground.

Seems obvious that some influence comes into play when dropping from the 28 to the .410.

The only appreciable difference I'd expect would come from differing pellet count. Same pellet count and same choke effect should equal the same pattern diameter nominally.

My "Personal Opinion" until proved otherwise is the major factor here is the much higher percentage of the shot which come under direct influence of the choke.

I don't think choke contact is an issue. Even though shot acts only as a semi-fluid, it seems to me that choke effect is typical fluid reaction to a constriction/nozzle in a flow field. I would contend that all the shot is under direct influence of the choke. It is clear that the shot is more or less incompressible and will accelerate (front of the shot column to the back of the column as it flows through the constriction) to maintain mass flow rate. The only energy available to support this acceleration is the shot column internal pressure. The pressure drop will reduce pellet-to-pellet spring apart and will reduce the "sideways wind" of the air entrapped within the column. Thus, the pellets subject to more choke effect will have lower "sideways" velocities and will take longer to disperse compared to less choke effect.

DDA

Good post, Miller. Glad to hear you are feeling up to some shotgun research. Have you read "Performance of Sporting Shotguns" by Dr. Andrew Jones? He answers a lot of questions.

Shotgun patterns follow a Rayleigh distribution, which can be nicely approximated with a normal distribution. The Rayleigh distribution describes rifle groups, artillery fire, and bombing patterns, also.

I believe that you're wrong, Rocketman.

Hi, Charles. Thanks for taking the time to answer. Wouldn't be the first time I was wrong about something, but I don't think so.

Pix of shot columns emerging from barrels show the center of the mass poking ahead, not a hole as your explanation (front of the shot column to the back of the column as it flows through the constriction) would anticipate.

My "model" does not anticipate a hole in the shot column. It anticipates a longer shot column with lower initial dispersion. Look at the photos Drew posted and note that his photos and my model agree.

Also the choke effect is opposite of your view ( Thus, the pellets subject to more choke effect will have lower "sideways" velocities and will take longer to disperse compared to less choke effect) as the radial acceleration toward the bore center imparted to the shot is speed and constriction dependent - more of either making more choke effect.

I must disagree with your view of how choke works. The passage through the choke constriction is an orderly process. There is no inward acceleration as the pellets are accelerating forward and rearranging themselves to meet the instantaneous bore diameter. The pellets have no inward velocity at the muzzle. they have only forward velocity, pellet to pellet contact pressure, and internal air pressure. The pressures are exchanged for small accelerations,some of which are perpendicular to the forward velocity. Thus, we have a large forward velocity and a small sideways velocity. Absent aerodynamic forces, the trajectory is the resultant of the two velocities.

I find it difficult to accept that the air in the shot mass has any effect even in the least.

Keep in mind that the air is at stagnation pressure at or near sonic velocities. Said air will have some relatively high sideways velocities as it seeks to achieve ambient pressure.


did you read what you had written before you posted it?

Yes, I did and I stand by it until "enlightened." ;-}

Thanks for saying that. I don't believe I have ever heard another shooter actually mention ANY statistical distribution, much less the correct one. I approximate that with a bivariate normal distribution - simply because I've never found a proper transformation function for the Rayleigh. For most purposes the bv normal is close enough when testing rifles for precision. I'm afraid I have never done any statistical analyses of shotgun patterns - though maybe I should.

I still don't understand, even with pictures

Ed Lowry, ballistician and the director of research at Olin-Winchester, spark shadowgraphs. See "The Effect of a Shotstring" American Rifleman, November 1979.
The shells were likely the Winchester/Western Mark 5 with the polyethylene shot collar and fibre wads introduced 1961



Another images, the source of which I can't find. It appears to be 1 1/4 oz. Steel 5s = 304 pellets; possibly Kent Teal Steel at 1350 fps.

Cylinder at 30 yds looks like full at 50. The exact constriction is also unknown



I recall a discussion about coloring pellets; front, middle and back and taking images in flight as to change in location? Would probably need inside and outside also.

I recall a discussion about coloring pellets; front, middle and back and taking images in flight as to change in location? Would probably need inside and outside also.