All Choked Up
January 04, 2011
According to Layne, constricting the bore of a shotgun barrel is one of the all-time great ideas in shooting. Here's the rest of the story.
No one knows for certain who was first to discover that a slight reduction in the bore diameter of a shotgun barrel at its muzzle would increase its effective range. In the United States, the person is commonly believed to be famous trap shooter Fred Kimble of Peoria, IL, who began to experiment with the idea during the mid-1880s. Kimble, by the way, was also one of the early developers of the clay target and called his invention the Peoria Blackbird.
At any rate, before the light bulb shined brightly inside his head, a pattern fired by the typical shotgun had lost much of its effectiveness by the time it had reached 20 yards or so. The use of a choked barrel combined with eventual improvements in shotshell quality just about tripled its effective range.
The amount of choke constriction in a barrel is commonly expressed in either thousandths of an inch or in "points." It is easily determined by using a special device available from Brownells and other suppliers of gunsmith tools that measures the inside diameters of the choked section of the barrel and its main bore. Subtracting the former from the latter reveals the amount of choke in the barrel. For example, if the bore of a 12-gauge barrel measures .729 inch, and its choked section measures .694 inch, it has .035 inch, or 35 points, of constriction, which is Full choke for that gauge.
Top-quality chokes almost always deliver pattern diameters that closely agree with their markings, but lesser quality ones do not.
The actual bore diameters of barrels made by various manufacturers often differ. Of the 12-gauge guns in my battery, a Browning Citori over-under has the smallest bores at .715 inch, while a Remington 90-T trap gun measures the largest at .745 inch. But regardless of how a barrel measures, a gun is choked Full if its choked section is .035 inch smaller than its bore diameter. In the case of those two guns, a Full choke for the Browning has an inside diameter of .680 inch, while a correct Full choke for the Remington will measure .710 inch.
The amount of constriction in barrels is the same for a particular choke for all gauges up to a certain point, but once we move beyond open chokes used for shooting at relatively close ranges — as in skeet shooting — they begin to change. From there on, it becomes a matter of constriction percentage. As I mentioned, for the 12 gauge, .035 inch of constriction is considered Full choke nowadays. Assuming a bore diameter of .730 inch, this puts the percentage of constriction at roughly 4.8 percent. If we apply that same .035 inch of construction to a 28-gauge barrel with a bore diameter of .550 inch, we are at 6.4 percent, which is far too much. To arrive at the same 4.8 percent, or Full, choke for the 28 gauge, we would choose a choke with about .010 inch less constriction than for the 12 gauge, or .025 inch of constriction.
|Choke||10, 12, 16-ga.||20, 28-ga.||.410 Bore|
| Skeet ||.005||.005||.005|
| Modified ||.020||.015||.012|
| Full ||.035||.024||.018|
|This information was obtained from Briley Mfg.|
In the beginning, the amount of choke constriction in shotgun barrels was fixed, and the shotgunner who desired other constrictions had no choice but to buy another gun or buy another barrel for the gun he owned.
Then came barrel-attachment devices that enabled the owner of a shotgun to quickly and conveniently change from one choke constriction to another. One of the more popular was the Cutts Compensator, which was developed by U.S. Marine Corps veteran Col. Richard M. Cutts and later sold by the Lyman Gun Sight Corporation. It consisted of interchangeable tubes of various constrictions that screwed into the front of a vented cage, the rear of which was permanently attached to the barrel.
The Cutts Compensator shown here on a Winchester Model 42 skeet gun was one of the first devices designed to use interchangeable choke tubes.
Another popular device was the Poly-Choke, which used an adjustable internal collet to vary constriction. But the most interesting, and probably the least successful, was a contraption called the Adjustomatic choke system. It automatically self-adjusted to its next tighter choke setting with each firing of the gun, which probably did not work very well on an incoming bird. Since those devices and others like them were larger in diameter than the barrel, a lot of shooters did not like their appearance.
Interchangeable Screw-In Chokes
The interchangeable screw-in choke systems of today do not change the appearance of a gun, and that along with their affordable prices have made them quite successful. This idea is much older than most of today's shotgunners realize. During the late 1800s, firearms designer Sylvester Roper developed perhaps the first interchangeable chokes for muzzleloading shotguns. The tubes were actually shorter than today's chokes, and they screwed onto the outside of the muzzle rather than inside, but the idea was the same. The screw-in choke idea of today began to catch on in 1961 when Winchester introduced its Versalite system on the Model 59 shotgun, but it would be several decades before the idea was entirely accepted by hunters and some shotgun manufacturers.
Whether the screw-in choke is a great invention or just another gimmick we really don't need depends on how a gun is used. The chap who hunts nothing but ruffed grouse on the Upper Peninsula of Michigan can get by quite nicely with a fixed choke in either Skeet or Improved Cylinder in his pump or autoloader. If he shoots a double, one barrel in Skeet and the other in IC is likely all he will ever need.
Most skeet shooters live happily with a single choke, and the same applies to hunters who shoot liberated birds on preserves. But there are times when quick-switch chokes are great to have, and the turkey gun comes to mind.As a rule, the harder the shot, the more choke constriction can be used so long as pellet size is in the neighborhood of No. 4 or smaller. Pellet hardness in today's turkey loads ranges from relatively soft lead to the extremely hard non-lead loads. Depending on the type of shot in a particular turkey load, optimum choke constriction for the tightest and most dense patterns possible can range from .050 to .080 inch or somewhere in between, so having several chokes with different degrees of constriction enables the hunter to determine which works best for a particular load.
Before Layne had a set of eccentric chokes for his 28-gauge Model 12 custom made, it placed its patterns far to the left and above his hold point.
I cannot say how many chokes other shotgunners actually need, but I will say that for wingshooting, Improved Cylinder in a single-barrel gun and IC and Modified in a double nicely handle about 99 percent of my hunting. And this includes everything from shooting grouse in heavy timber and ducks over decoys where shots are usually close to shooting ringneck pheasants late in the season when birds are prone to flush at some distance from the gun. But there is no law against owning more chokes.
A 12-gauge Remington Model 11-87 I have used all over the United States and in South America has six chokes, and I don't recall ever needing more. Their constrictions are .005 inch (Skeet), .010 inch (Improved Cylinder), .020 inch (Modified), and .030 inch (Light Full). The other two chokes have .055 and .070 inch of choke, both used for head/neck shots on spring gobblers — the former with Hevi-Shot, the latter with Xtended HD shot. I don't hunt deer with that shotgun, but if I did, I would add a rifled choke to the bunch.
The two basic types of screw-in chokes are the flush-fit and the extended. A choke that extends a bit beyond the muzzle has a couple of advantages. For one, it protects the muzzle of the barrel from damage should it accidentally strike a rock or other hard object in the field. The extended choke is also easier to check for looseness than a flush-fit choke, and this is especially important on a clay target gun that is subjected to the firing of many rounds in a day. Markings or color-coding on the outside of extended chokes make it easy to tell at a glance what choke is in the barrel.
The biggest disadvantage to interchangeable chokes is they are less trouble-free than fixed chokes and require more maintenance. This should go without saying, but I will say it anyway: Everything I am about to recommend should be done with the gun completely unloaded.
With that said, the first rule to remember is never allow a choke to become loose in the barrel. Shooting a gun with a loose choke will likely damage its threads and those in the barrel as well. During long shooting sessions, I check a choke for tightness every 100 rounds or so. If I shoot less than that, I check it at the end of the day.
It is also important to remove a choke and thoroughly clean its threads and the threads in the barrel each time the bore of the barrel is cleaned. An old toothbrush dipped in bore solvent works fine. Just as important, allowing rust to form on the threads can cause a choke to seize in place and become impossible to remove. This is easily prevented by coating the threads with a light grease after it is cleaned. Special lubes designed specifically for this purpose are available from several sources, and in a pinch, those formulated to prevent breech plug seizure in muzzleloading rifles will also work.
It is important to keep a choke tight in the barrel when shooting and to occasionally clean fouling from its threads and the threads of the barrel. A good grease designed for the purpose applied to the threads after cleaning will prevent the choke from becoming impossible to remove by conventional means.
Don't forget to use a brass brush and solvent to remove powder fouling and any buildup of plastic residue left behind by the wads found in most of today's shotshells. The plastic tends to build up quite heavily during high-volume, hot-barrel shooting, and when that happens, the choke is easier to scrub clean by removing it from the barrel. But here's a word of caution: When cleaning a choke, never place it in a bench vice because doing so can squeeze it out of round, making it impossible to screw into the barrel. Wearing an old glove will protect the hand holding the choke for cleaning from the bore brush.
Keep in mind that shotguns don't always deliver pattern diameters at various yardages that agree with the markings on their screw-in ch
okes. A 28-gauge over-under I once owned came with chokes marked "Improved Cylinder," "Skeet," "Modified," and "Full," but in measuring them, I found the IC choke to have no constriction at all (Cylinder Bore), the Modified choke was actually Light Skeet, and the Skeet choke was .006 inch larger than the bore of the gun- — a blunderbuss choke?
Measuring bore and choke diameters can be informative, but the sure-fire way to determine if a particular choke is delivering the type of pattern needed for a particular hunting or shooting application is to check it and the load to be used at the pattern board. If it's wingshooting, first determine at what range most of your shots are taken. Then, try various chokes at that distance to find the one that delivers patterns of the largest diameter but with densities great enough to assure multiple pellet strikes to the bird you will be hunting.
Regardless of whether the shotgun you own has fixed or interchangeable chokes, you can believe me when I say that constricting the bore of a barrel is one of the all-time great ideas in shooting. Without it, most birds that manage to put more than 25 yards or so between them and the shotgunner before he squeezes the trigger would live to fly another day.