By Tom Roster
One cannot be a shotgunner and avoid the topic of choke. After considering which gauge and load to fire on any given day, the biggest decision left is always what choke(s) to use.
Photographed by Chris Siefken
Choke has three component parts: 1) choke constriction, regardless of whether the choke is fixed (integral) or screw-in, 2) the pattern produced by the choke itself, and 3) the influence on pattern by the load chosen to be fired through the choke. Shotgun and screw-in-choke manufacturers have confused this issue almost beyond understanding by not agreeing to universal choke-dimension standards but then applying consistent names to chokes anyway, such as Full, Modified and Improved Cylinder or ¾, ½ and ¼, implying universality.
This obscures the fact that each choke of the same name will vary in configuration and dimensions among manufacturers and thus will pattern differently. All that can be counted on is that a choke of a given name approximates the manufacturer’s idea of the relative constriction within its given model line. It’s the shotgunners who then believe that such choke names can be expected to produce known pattern qualities. But those who take the time to actually pattern-test chokes and loads quickly learn that most assumptions about pattern qualities and choke labels often do not meet expectations.
The Physical Choke
First consider the physical choke. If it’s a screw-in choke, it’s basically nothing more than a short piece of threaded steel conduit; if it’s a fixed choke, it is simply a short constriction of the internal diameter of the barrel. Both types force the shot charge to become narrower than the bore itself. In a nutshell, this is the total effect of choke. But the effect is wonderful. By narrowing the shot charge just behind the muzzle, the charge prints smaller-diameter patterns with greater pellet densities at any distance than if there were no choke at all. This allows greater ranging lethality.
Assuming that all loads are equal (and they certainly are not!), shotgun literature leads one to believe that Full choke prints tighter patterns than Modified choke, which in turn prints tighter patterns than Improved Cylinder. To the undiscerning, this is taken as gospel. But to the discerning shotgunner—one who assiduously pattern-tests—the reality is that there are many exceptions to this generalization. The pattern-tester also quickly learns that one manufacturer’s so-called Full choke does not necessarily pattern the same with any given load as another manufacturer’s Full. The same thing often can be said of so-called Full chokes among different models of shotguns from the same manufacturer. This is also true of any other named chokes currently in vogue.
The discerning shotgunner also learns that there are all sorts of different lengths, configurations and internal diameters yielding different constrictions for one manufacturer’s Full choke versus another’s. It is the same for all other chokes, whether they use a word or fraction name. By constriction, I mean the difference in diameter between the actual bore and the choke zone. Due to the lack of agreed dimensions, if you mic a rack of 12-gauge guns, you will find a wide divergence in the constrictions for Full or any other choke designation.
By configuration, I mean the angle and length of the forcing cone that leads from the bore into the constriction area of the choke and whether or not the choke contains a parallel section—and if so, the length of that parallel section. The dimensions here also vary widely among manufacturers. Of course, if the choke is conical in configuration, it is essentially one long forcing cone, with its narrowest point right at the muzzle. Pattern-testing reveals that for a given constriction, chokes that contain parallel sections almost always pattern more tightly at long range than conical chokes. Parallel chokes also tend to pattern large shot sizes (larger than No. 5) more tightly at long range than conical chokes.
Also, if you pattern-test, it becomes apparent that most imported chokes do not have anything over American chokes; often it’s just the other way around. The point is: If you’ve purchased a choke by a “big name,” don’t assume that it will yield magical patterning results. One does not know what any choke will do until it is correctly pattern-tested with the actual loads intended to be fired through it.
As to extended versus flush-mounted choke tubes, I never have found improved patterns from extended tubes. But trust me: There are many shotgunners who believe that extended tubes give them improved patterns. (These individuals generally don’t pattern-test!) All that counts is the overall length of the choke area. And the same overall length can be had fully inside the barrel or partially extending outside of it. Also, I never have measured any patterning improvement from ported tubes. And the short surface area available for porting on extended tubes is too small to cause any appreciable reduction in muzzle lift either.
Consult a variety of shotgunning sources, and none will agree on exactly the patterning percentage that, say, a Full versus a Modified versus an Improved Cylinder choke should produce at the standard patterning distance of 40 yards. But if we averaged their opinions, it would be something like Full should produce 70%-or-better patterns, Modified 60%-or-better and Improved Cylinder 50%-or-better. Working from this, can you count on your chokes marked Full, Modified or Improved Cylinder to deliver these percentages with your chosen loads? No, you cannot, unless this is proven by pattern-testing. Those who take the time and effort to pattern-test find a much greater divergence from this patterning dogma. Many times I have found that a variety of chokes—integral or screw-in—that were designated Modified actually produced denser patterns with shot sizes BB and larger than the same chokes from the same manufacturers that were designated Full. I have found this to be especially true with steel shot.
While with lead and bismuth shot my pattern-testing has taught me that you generally can count on different manufacturers’ Improved Cylinder chokes to pattern more openly than their Modified chokes and so on, this seems to be a reliable result only with shot sizes smaller than No. 4. Once you get above No. 4s in soft or hard shot, this stair-step patterning performance starts to break down. Therefore, the wise shotgunner always will take the time to pattern-test his chosen loads through his chosen chokes, especially if those loads involve pellet sizes larger than No. 4 and he is looking for reliable and lethal patterns beyond 40 yards.
In this same vein, if every shotgunner held fire when birds or clay targets flew beyond 30 yards, all of this complexity and breakdown in patterning expectations versus choke designation would disappear. At 30 yards or less I have found that chokes behave consistently according to stair-step expectations, with open to tighter to very tight constrictions yielding ever-tighter patterns with all shot sizes and types.
Last but not least, the knowledgeable shotgunner can select loads to manipulate patterns with particular chokes. With lead loads, for example, by going to higher-antimony shot and then the next step up—buffered lead—pattern percentages can be increased significantly for any given choke. In addition, by carefully pattern-testing different shot sizes in a particular choke, one can discover which size patterns best. One also can use spreader loads and soft lead shot to open patterns in any given choke. When it comes to bismuth, Kent’s new bismuth shot has patterned better than traditional sources of bismuth shot in my tests. In hard shot types, HEVI-Shot always has out-patterned steel in my tests. And just as with lead, certain shot sizes of steel or HEVI-Shot pattern better through certain chokes than other sizes. So switching shot types and sizes can affect patterning performance considerably for any given choke.
So that’s it. My advice: Assume nothing about how any choke will pattern with any given shot type, load and shot size. You must pattern-test to measure and find the truth about any particular load-and-choke combination. There are no shortcuts.
To correspond with Tom Roster or to order his reloading manual on buffered lead and bismuth shotshells, his HEVI-Shot reloading manual, his updated 75-page Shotgun Barrel Modification Manual or his instructional shooting DVDs, contact Tom Roster.