Standardized Patterning Method

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. 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.

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.

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. As a matter of fact, that’s the norm.

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. Any choke stamped “Modified” will probably throw a 60% pattern with something.

Oberfell and Thompson were highly regarded as doing some good mathematical models of patterning, but some further work by others has introduced new models.

I don’t for a moment think that anything I have said answers your questions, but it should help get you started. I’d love to hear what you come up with.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC

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1 Response to Standardized Patterning Method

  1. Ed Sybert says:

    If Josef will look up “Neil Winston shotgun patterns” I believe he will find some excellent information on the subject. Neil developed a method of patterning at 13 yards that is widely used for testing Point of Impact (POI). He also published information on chokes and resulting patterns. -Ed


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