Even More On Patterning

Dear Technoid;

I have enjoyed reading your columns and contributions over the years to the various shotgun periodicals covering the technical aspects of shotgun shooting. I have some questions related specifically to shotgun patterning that I hope you can answer:

Is there a standardized method of shotgun patterning execution and analysis that is considered an industry standard. I am a construction engineer by profession and deal with references made to ASTM, AASHTO, ACI, ….etc.? Is there such a reference?

What resources are available that describe patterning theory and practice? Any available literature references would be helpful.

What is the purpose of patterning? To determine if pellet density is uniform within a given area? To determine point of impact?

How should the shotgun be mounted during the test? Shoot as if you are shooting at a moving target or use a bench rest?

With current technology for chronographing so easily available, should it be included in a proper patterning exercise?

I would be grateful for any direction you could offer. I would like to learn as much as I can about proper patterning.

Thanks for your time and consideration.

Best Regards,

Dear Josef,

In reading your question, I realize that it will take a book to answer it. Rather than do that (I want to go shooting this afternoon instead), I’ll quickly show you some of criteria for patterning (or lack thereof) and a few of the questions it raises.

It is amazing, but patterning a shotgun really hasn’t been absolutely standardized. It’s still in the “whiter, brighter, better” stage if you read some of the ads.

Everyone in the US (foreign countries differ) seems to agree on the following: A 12 gauge shotgun is “officially” patterned at 40 yards from the muzzle. The gun is aimed like a rifle at a mark. After the shot is taken, a 30″ circle is drawn around the pattern so as to include the largest possible number of pellets. The pellets in the cartridge are counted and the pellets striking within the 30″ circle are counted. The percentage of the load’s pellets which hit in the 30″ circle comprise the pattern percentage.

At this point agreement stops. There is no hard and fixed number for what percentage comprises a “skeet”, improved cylinder, modified or full choke. Different sources publish different numbers. I’ve seen Improved Cylinder described as anything from 40% to 60%. Clever manufacturers are always coming up with new names for new chokes. The most recent are the Sporting Clays #1-#4 chokes, called SC1 etc. There is also a Skeet 1 and 2 as well as various trap and turkey designations. It’s all marketing.

The problem is exacerbated by the proliferation of screw-in chokes. Manufacturers feel that they can sell more if they come up with a new name for each and every .005″ of additional constriction. After all, if they sell a certain constriction, there ought to be a name for it if someone’s going to buy it.

Compounding this is also the fact that many overbore barrels, now becoming popular, produce a given pattern percentage with less choke constriction, so you can’t just say that everything with .010″ constriction is an improved cylinder choke. In certain bores it will pattern modified.

Then you have to add in the fact that different shotshells pattern differently. One brand of 1-1/8 oz target load may not pattern within 15% of another brand with the same shot size and pellet count even though they are both coming out of the same barrel and choke. Additionally, it is not at all uncommon for shells within the same box to have patterns which differ 10% or more.

The ONLY constant in patterning is the final pattern percentage. The percentage of shot within a 30″ circle that your barrel/choke/shell combination throws is its pattern. Unfortunately, in order to determine that you actually have to do the pattern testing. Shooters are notoriously reluctant to do that kind of work, so they would rather read what is stamped on the choke and believe it. Since a shotgun pattern is such a random even anyway, this probably isn’t all bad.

The whole purpose of determining choke is to be able to predict pattern density at a given distance. In order for this to mean anything, the shooter has to know how big his target is in square inches (rabbit, bird, clay target) and how many pellets of a particular size it will take to kill it. Then he has to know what pattern percentage at 40 yards will give him that pellet density per square inch at the distance at which he is actually shooting. Obviously all this is impossible for the average guy and probably useless considering the quickly varying distances of clays and game, though trap and skeet, with their fixed distances, do lend themselves to more accurate study. Face it, for all practical purposes, in shotgunning there are only three distances- near (about 20 yards), normal (about 30 yards)and far (about 40 yards- considered to be the humane limit of most shotguns). Knowing that doesn’t stop me from carrying a pocketful of screw chokes because I enjoy fooling with them.

Oberfell and Thompson did a great deal of work on this forty years ago, as have many others. Ed Lowry has an interesting computer program on it. Ads for it are occasionally in the clay target magazines. The Germans did a lot of work at Wanasee years ago. Also the US ammo companies, particularly Winchester. Of course, the German and American standards are different. Naturally.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error, never in doubt.)

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1 Response to Even More On Patterning

  1. Ed Sybert says:

    I have patterened my shotguns and loads for over 40 years. The best information I’ve seen to date on the subject can be found here: http://claytargettesting.com/index.html
    In my experience the most valuable information that you can get from patterning is the center of impact with respect to your “aiming” point (we don’t normally aim shotguns except for special purposes like hunting with slugs or for turkey, etc.). For you to score well on clays or flying live birds, you must know if the pattern centers where you want it to; generally where your eyes are focused (on the target). Good luck, Ed


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