Understanding Patterns, or Trying To

by Terry Wieland

The least understood aspect of shotgunning is shot patterns — the scattergun equivalent of rifle accuracy, but more complex.

In an age in which we have interchangeable choke tubes with constrictions measured in thousandths of an inch rather than the traditional Improved Cylinder (IC), Modified (M) and Full (F), you’d think we would understand patterns more, not less.  But, such is not the case — not if shooters’ faith in different choke constrictions is anything to go by.

The shooter is Vicki Ash, with Wieland. You can plainly see the core of the shot pattern in the air. Milliseconds later, the clay turned to dust.

Over the years, many writers have tried to explain choke in all its complexities, and attempts have been made to illustrate the effect of a particular choke at a specific distance. To my knowledge, the people who have made the most concerted effort in this regard are Gil and Vicki Ash, two shooting instructors from Houston.

The accompanying photographs show the results of firing thousands of rounds and counting hundreds of thousands of pellet holes in patterning sheets, then translating the information into three-dimensional models showing what a specific pattern looks like at various distances.

shot patterns
The broad shape of patterns can be seen from Ash’s models. The rear view shows both the distances represented by each board, and the shape of the pattern after it passes its widest measurable point.

The problem has always been that a pattern is both three-dimensional and dynamic, and moves so quickly it’s impossible to see. To say simply that a full-choke gun places 70 percent of its pellets inside a 30-inch circle at 40 yards is so simplistic as to be misleading. That may be the yardstick, but by itself it means little.

Imagine the pattern as a cloud of pellets, ever-changing as it flies through the air. Then think in terms of the length of the cloud and the density of shot concentration within it. Finally, it can be judged as an effective pattern at various distances.

Gil’s models make it obvious the two most broadly useful chokes are Improved Cylinder and Modified, with the latter probably the least appreciated, but overall the most effective, of them all. The Modified pattern does not spread quite as wide as IC, but it maintains its shape far longer.

I have an H.J. Hussey box-pigeon gun made in London around 1910, barreled by Frank Squires, one of the best barrel makers of the era.  It has what are known in England as “tulip” chokes, and here as “jug” chokes. The standard measurement of constriction would indicate light Mod. and heavy Mod, but in actual use they deliver patterns both wide enough for skeet and usable for trap, including 16-yard and handicap. As an experiment, I have shot trap from 27 yards and done as well with that gun as with my dedicated trap gun and extra-full chokes.

One of the most surprising of the Ashes’ findings is that, regardless of choke, there is a core pattern that extends from about ten yards from the muzzle too far beyond normal measuring distance. Choke constrictions affect only the outer pellets in the pattern, not the center ones, which constitute 30 to 50 per cent of the shot count. This central “core” flies out from the muzzle as a pipe of shot about 12 to 15 inches in diameter. This is why you can get the odd inexplicable kill at 50 yards with even a Cyl. choke (a shot you should not be attempting anyway, but I use it as an example.)

It’s as if every choke constriction includes a central “extra full” component which kills or breaks if you’re dead on, leaving the outer pellets to do the job if you’re not. Those outer pellets can be spread farther or closer, depending on whether you’re using IC, Mod., or something else.

As Gil’s models also show, most chokes have one distance where they are most effective, falling off rapidly after that, with Modified being the exception.

For more information, you can find Gil and Vicki Ash at their “Optimum Shooting Performance” (OSP) school (https://ospschool.com). They have books and DVDs, an extensive archive of their work, and some videos available on YouTube.


Terry Wieland has been Shooting Editor of Gray’s since 1993 and is the author of a dozen books on hunting, shooting, and history. His latest is Great Hunting Rifles — Victorian to the Present, published by Skyhorse in 1997. Last year, Skyhorse reprinted his acclaimed 1999 book on Robert Ruark, A View From A Tall Hill.