Rules of Shotgun Choke Constriction

By Randy Wakeman

While we might think high percentage patterns are something new, that is not the case. 106 years ago, William. L. Robedee achieved over 90%, 30 inch patterns at 40 yards with his progressively tapered shotgun barrel, which he patented in 1906. This compares to roughly 75% patterns from conventionally choked barrels with the same maximum constriction.


I. Background


While there are no standards or rules for constrictions in choke tubes, there should be. No other component of a choke tube makes more sense or has such a clear effect on pattern diameter. Over the years, all kinds of observations and theories have been set forth. Few make any sense, much less pass the test of providing sharable data.


Part of the problem is the subject matter itself. What we have tried to do is apply exactitude to something that is intrinsically inexact. Back in January of 1956, Col. E. H. Harrison published "A ‘New’ Method of Evaluating Shotguns" in the American Rifleman, describing the superior German method of evaluating patterns from 1893. The patterns were segmented into 100 parts; the targets called "100 field targets." It was an extremely precise method of evaluating patterns that was found to be too precise to be of value, due to shot to shot variations. The Germans used a 75 centimeter circle at 35 meters range. While it gave tremendous data at that 35 meters range, it did little to show what pattern performance might be at other hunting ranges. The Germans went back to work, resulting in a huge body of data assembled and finally approved in 1937.


John Brindle determined that it is not possible to have an effective spread with a 12 gauge 1-1/8 ounce shotshell larger than 25 inches across at any range. That calls into question the value of using a 30 inch circle to define patterning performance. Still, you have marketing attempts referring to the “critical 30 inch kill zone,” with large diameter shot, although there is no such thing. Don Zutz commented on the “tightening effect” of certain propellants on patterns, particularly Green Dot. With a small sampling or by cherry picking data, all kinds of erroneous conclusions can be reached.


Shot itself is inexact. The flight characteristics of hundreds of pellets, colliding with each other, the wind, pellets of varying sizes, various velocities, varying eccentricities and varying densities makes for a potentially quite random event. How round are the pellets in your shell? What is the muzzle velocity of the next shot? How consistent are your shotshells over, say, 500 rounds? No one knows. Since we don't know, it is all the easier for a manufacturer of a shotgun or shotshell to claim anything. All you have to do is say words to the effect of “We believe it is the best patterning thing you've ever seen” and away it goes.


II. Past Results


While all kinds of claims are continually made, few have an objective foundation. If you think global warming is confusing or a hoax, a subject studied by actual scientists, then what chance does a shotshell pattern have? They are, by nature, so inconsistent that one pattern is meaningless. It takes five, ten, or more patterns to give a reasonable basis for comparison. The frustrating thing is that we are hoping one shell, the next shell, is the shell that drops the turkey, yields a dead in the air pheasant, or breaks that clay target. Not the next five or ten shots, the single next shot. That is another problem with patterns, as they are averaged past performances, not future results.


III. What Doesn't Work


Forcing cones, back boring, cryogenics, changes in harmonic vibration: none of these interesting approaches has proven to do anything substantive. It isn't easy to prove a negative, so a clinical disproving is equally hard to come by. Neil Winston (and others) have shown that elongated forcing cones and back boring have both thinned patterns and produced lower velocities with Perazzi and Remington test guns.


The human factor and the placebo effect are invariably at play. As long as we persist in trying to read breaks, there is little hope. How often have you heard the lament, “I used my new choke tubes and my scores went down!” Where would we get the idea that a choke tube makes us a better shot? If you have ever bowled, you know that your score isn't the same every game, even though you use the same ball on the same lane. If a baseball infielder muffs a grounder, is it usually a “bad glove”? Wide receiver drops the football--bad football? Like anything else involving humans, we all have better personal performance days than others. The good news: it is hard to overdose on placebos.


IV. What Works


We do know what works and we do know that accuracy and consistency are synonymous. We know that perfectly spherical shot behaves more consistently than malformed shot or odd shapes. We know that buffering improves pattern percentages and we know that higher velocity loads open patterns. We know that larger diameter shot yields higher percentage patterns than smaller shot, which is a mixed blessing, as larger shot means less pellets for the same payload.


We know that wad design affects patterns. There are spreader loads that clearly work and non-slit wads that pattern more tightly with less constriction than slit wads. We know that the best patterns are produced by both high-quality shells and high-quality chokes; you can't have the best patterns without both.


V. Why Constriction Matters


The difference between the barrel inside diameter and the smallest choke inside diameter is the constriction. A constricted end of the barrel is what choke is, back to the days of Fred Kimble and the early choke bored barrel. When it comes to “improving” patterns, improving means smaller diameter and therefore tighter patterns, as in “Improved Cylinder” and “Improved Modified” creating smaller diameter patterns than standard cylinder and modified chokes. It mattered when the notion of choke was popularized by Fred Kimble and it mattered when William Robe patented his 90%+ pattern percentage shotgun barrel.


Even though such products like Federal Black Cloud and Federal Heavyweight turkey loads rely on the non-slit style of wad to achieve tighter patterns than a conventional wad, the amount of constriction remains important. These two loads, though wildly divergent, actually need more constriction to get the tightest patterns, not less, as choke maker George Trulock has discovered.


Though "improving" a pattern means a tighter pattern, historically, it was rarely the goal. The goal is the largest effectively dense pattern, not the smallest, for the specific range and purpose. An "improved modified" level of performance is no improvement at all in American Skeet; it is the opposite of what close range shooting with a high pellet count requires.


The marking on a choke tube or on a barrel does not equate to a specific pattern density. It doesn't even mean a precise constriction, as measuring a variety of factory choke tubes will quickly reveal. We still have to visit the patterning board, where the protocol is to start with a mild constriction choke and increase the constriction until we have the largest diameter pattern that we feel is effective for our purpose, with that specific shell, in our specific shotgun.

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Copyright 2012 by Randy Wakeman. All rights reserved.