Getting a Hold on Choke
The right shotgun choke helps prevent crippling in the field.
By Henry Chappell
You’re into your third covey before midmorning, and you’re on. The birds are holding; the dog is handling well; and you’ve used your second barrel only once so far — to take a double on the last covey rise. Now the singles are spread nicely about a sage flat. Your pointer locks up, and you stride past her, brimming with confidence. Your initial flushing attempt produces nothing. You assume the birds ran or flushed unseen, so you give the dog the “right on,” command. She doesn’t move. You repeat the command. Her eyes bulge.
OK, you’ll humor the old girl. She’s proved you wrong before. More stamping and shuffling and no bird. As you turn to look back at the dog, a single bobwhite flushes 15 yards ahead of you — well beyond where you expected it to be. Your gun comes up smoothly; you’re only dimly aware of the recoil, but instead of the puff of feathers and tumbling bird, you detect only a slight wobble. The bird is quartering away, maybe 30 yards out, when you touch off the second shot. A couple of feathers fly, but the quail glides into heavy scrub 60 yards distant.
Your dog marked the bird, and you’re behind her yelling “Dead! Dead!” as if she doesn’t know her job. There’s nothing to do now but wait and hope as she rams around in the cover.
The picture looked right, just like the countless clay targets you broke during the off-season. But this bird was a little farther out than low house seven. And how many of those targets did you powder and how many did you merely chip or crack? It’s all the same on the skeet field. But now the stakes are higher.
The dog flash-points, then dives into a clump of bluestem. After a short chase, she brings the bird. You’re proud of her, of course, but you would rather have had the bird fall instantly when you shot.
So what happened? Poor shooting? Perhaps. Even the best shotgunners occasionally falter. In this case, the bird obviously caught only two or three pellets, and those didn’t do the job. Do you know what your shot pattern looks like at 25 yards? Or even more critical, how does it look out toward the edge of effective shooting range? Too many hunters have no idea and probably would be surprised — or hor-rified — to find out.
A Pattern Emerges
Shotgun patterns are controlled primarily by choke, which refers to the amount of constriction relative to the diameter of the bore of the gun barrel. In simple terms, this constriction, placed near the muzzle, compacts or concentrates the shot column, creating a denser pellet swarm and, up to a point, greater effective range. For a given bore diameter, the greater the constriction, the tighter the pattern.
For the 12 gauge, which has a nominal bore diameter of .729 inches, choke constriction usually increases in .005-inch increments. For instance, .005 = skeet, .010 = improved cylinder, and so on. Choke constriction decreases along with gauge. For the 20 gauge, which has a nominal bore diameter of .615 inches, choke increases in increments of .004 inches.
Although the chokes in older shotguns typically are fixed, most of today’s production shotguns come equipped with interchangeable, screw-in choke tubes. To meet the demands of competitive shooters, aftermarket manufacturers offer choke tubes in a dizzying variety of styles and advertised performance. All strive for the same goal: to control the shot column so that when it leaves the muzzle of the shotgun, it expands into an efficient pattern of a certain diameter at a certain distance. A competent gunsmith can fit most older shotguns with choke tubes.
“There are only two kinds of chokes,” says Carrollton gunsmith Ron Coleman. “Those that put the pattern you want where you want it and those that don’t.” Coleman, who specializes in fine shotguns built by custom gun makers such as Holland & Holland, stresses that although choke may be expressed in inches of constriction, actual performance must be measured on a patterning board.
Traditionally, the practical measure of choke has been expressed as the percentage of pellets in a given load in a 30-inch circle at a range of 40 yards. Ballisticians quibble about the exact numbers, but in general, choke can be defined by the percentages in the list below.
- Super Full: 80-85 percent
- Full Choke: 65-70 percent
- Improved Modified: 55-65 percent
- Modified: 45-55 percent
- Improved Cylinder: 35-45 percent
- Skeet: 30-35 percent
- True cylinder (no choke): 25-35 percent
To pattern your shotgun, tack up a piece of paper roughly 40 inches square and draw a quarter-sized aiming point in the center. (A scrap of plywood or particleboard and the backside of cheap wrapping paper work great.) Pace off 40 yards, then mount and fire the gun at the aiming point. Don’t be surprised if the pattern isn’t distributed evenly around the bull’s-eye. Draw a 30-inch circle around the densest part of the pattern. (A marker tied to a 15-inch length of string, tacked to the center of the pattern, or a 30-inch circle of plexiglass works well.) Count the number of pellet holes within the circle, marking each so you’ll know which ones you’ve counted. Now compute the percentage by multiplying this number by 100 and dividing by the average number of pellets in the test load. (See sidebar for pellet counts.)
Coleman fires dozens of test shots when measuring the performance of a given shotgun-choke-load combination. “You can take a gun with a certain barrel and tube and shoot it four or five times and it might show a bias toward the upper right-hand quadrant,” he says. “Then, all of a sudden, it will change. It could have something to do with the way the pellets are dropped into the shell or any number of things. No one really knows. But for the average hunter, at least three individual shots at a patterning board are necessary to get an average of pellet strikes.”
Beginning shooters and veterans with their first set of interchangeable chokes may be surprised to see their new tubes designated as one choke for lead shot and another for steel. That’s because for a given constriction, the resulting pattern varies wildly depending on shot hardness. In general, the harder the shot, the tighter the pattern. Patterns also vary depending on shot-cup design and powder-burn rate. Thus, 1-ounce loads of No. 8 shot of a certain hardness may pattern differently from one brand of shell to another.
Steve Power, sales manager with Houston-based Briley Manufacturing, emphasizes the point. “A number of choke tube manufacturers, including Briley, still go by the Old World definition of choke. That is, constriction relative to bore size. But with the plastic shot cups and hard shot used in modern ammo, a modified choke may produce something closer to a full choke pattern.”
In other words, you may have to vary choke tubes and loads until you achieve the desired pattern.
Of Shot Strings and Columns
Hunters patterning their guns for the first time may be shocked by the patterns thrown by the cheap shells bought by the millions every year just before the dove season opener. Fortunately, they’re usually adequate at moderate ranges. But at longer ranges, more efficient patterns can mean the difference between clean kills and crippling. Just remember only to take shots within your effective range.
But the patterning board tells only part of the story. Forget the uniformly expanding cone pattern often used to depict shotgun operation. Instead, picture a sausage-shaped shotstring. (The pellet swarm is called a shot column as it travels down the barrel, a shotstring after it exits the muzzle.) In other words, the pellets in that reassuring, yard-wide pattern don’t all reach the target at the same time.
Think a long shot string gives you a little extra margin for error on those crossing birds? Consider a shot column as it travels down the barrel of a shotgun. When the primer ignites the gunpowder, the burning gases exert tremendous pressure on the rear pellets, deforming them as they push against the next layer. The softer the shot, the more severe the flattening. Further pellet deformation occurs as the column accelerates through the constriction of the choke area where the outside pellets are forced inward.
The pellet swarm leaves the muzzle more or less intact, but the shot string quickly expands and lengthens as air resistance causes the flattened pellets to fall behind. Because there is less air resistance behind the leading pellets, the bulk of the shot concentrates near the front of the string, while deformed pellets fall farther and farther behind.
While a long shot string may yield a slight advantage on the skeet field where a single pellet may chip and “kill” a clay target, a duck flying into the rear of a shot string may be crippled, especially at long range. The longer the shot, the more severe the effect, since the rear pellets lose energy more rapidly than those concentrated toward the front.
Most choke-tube designers minimize shot stringing by lengthening their tubes and employing a more gradual constriction which lessens pellet distortion. Hunters can gain further improvement by shooting high-quality ammunition. It makes little sense to buy top-of-the-line choke tubes and then shoot cheap ammo loaded with soft lead shot.
So you’ve patterned your gun, and your tubes perform as advertised, and you’ve matched each one with loads that consistently produce nice, even patterns. Which ones should you use?
Hunting for close-range upland birds such as bobwhites and woodcocks can be covered nicely with double-barreled guns choked improved cylinder and modified. Improved cylinder is a fine compromise for single-barrel shotguns.
Most dove hunting situations call for improved cylinder and modified choke. Straight cylinder or skeet choke can be advantageous for close-range shooting over stock tanks.
With steel shot, improved cylinder works well for waterfowl hunting over decoys. Long-range pass shooting with steel shot is best done with modified choke. With the other types of nontoxic shot, go with modified choke over decoys and full choke when pass shooting. Some experts do not recommend shooting steel shot through a full choke because steel shot columns may not conform to chokes as well as lead. However, modern-day steel shot ammunition is typically protected in the shot column by thicker wads; therefore, a full choke should be an acceptable choice for longer shots.
Today’s manufacturers produce specialty choke tubes optimized for long-range shooting at ducks and geese. These designs employ light-modified to improved-modified constrictions optimized to produce very tight patterns when used with hard, non-toxic shot such as steel, tungsten and Hevi-Shot. Bismuth shot, though non-toxic, is relatively soft and patterns much like lead shot.
Turkey chokes are designed to throw full to super-full patterns at 40 yards, while most of the pellets are concentrated in the central 15 inches of the circle. These chokes are preferred for taking shots at the stationary to slightly moving head of the wily bird.
Tradition aside, for those willing to burn some powder and endure bruised shoulders, there may be a better way to match chokes to hunting requirements. Coleman recommends patterning at typical hunting distances. “Tweak the ammunition and choke until you get roughly a 100 percent pattern spread evenly over a 30-inch circle at the range you’re most likely to see in the field,” he says. For example, a quail hunter would want a very dense 30-inch pattern at about 25 yards. A duck hunter might want a dense pattern at 35 to 40 yards.
Hunters should know the capabilities of their firearms. A serious big-game hunter wouldn’t dream of going afield with a rifle that hasn’t been sighted in. Shotgunners should be no less exacting.