Saturday, 30 August 2008 16:07

Shotgun Chokes

Count yourself lucky that some genius invented the screw-in shotgun choke. Otherwise, you’d probably need five shotguns.

Adjustable shotgun chokes give you the ability to change the pattern of your shot by tailoring the constriction. The baseline constriction is cylinder -- or the inner diameter of your barrel. From there, the designations grow tighter. 

Choke Bore Sizes and Constrictions
12 Bore .000 N/A .005 N/A .010 .015 .020 .025 .030 .035 .040 .005 and Rifled!
20 Bore .000 .003 .005 .007 .009 .012 .015 .018 .021 .024 .027 .005 and Rifled!
28 Bore .000 .003 .005 .007 .009 .012 .015 .018 .021 .024 .027 N/A
.410 Bore .000 .003 .005 .007 .008 .010 .012 .014 .016 .018 .020 N/A

(Courtesy of Briley Mfg.)

CYL = Cylinder
LTSK = Light Skeet
SK = Skeet
IMK = Improved Skeet
IC = Improved Cylinder
LM = Light Modified
M = Modified
IM = Improved Modified
LF = Light Full
F = Full
XF = Extra Full
D = Diffusion
N/A = Not Applicable

Looking at the chart, you’ll see that SK (skeet) imposes a .005% constriction compared to cylinder. Full gives you a .035% constriction. Yes, that’s a 600% difference.

Percentage of Constriction Based on Distance
Choke 20 Yards 30 Yards 40 Yards
Cylinder 80% 60% 40%
Skeet 92% 72% 50%
Improved Cylinder 100% 77% 55%
Modified 100% 83% 60%
Improved Modifiedz 100% 91% 65%
Full 100% 100% 70%

In this chart, you’ll notice that as the choke grows tighter (from cylinder to full) the density of the pattern increases based on distance.

That’s because tight chokes distribute the shot in a tight, dense pattern best for long shots. Open chokes give you a wider, diffused pattern intended for close shots.

If this sounds counter-intuitive, here’s the way it works.

You may be thinking that you want the wider pattern for longer shots because the target is further away. The longer the distance, logic dictates the wider the pattern giving you a better chance to hit the target.

But what you’re not taking into account are the laws of physics.

Smaller shot (which tends to be used for close shots of 16-20 yards) lacks the energy (momentum) to give you accuracy at longer range. The shot spreads willy-nilly and you lose accuracy.

So if you’re going for a long shot, you want to use a bigger pellet in a tighter shot string for an arrow-head effect. Hence, a tighter choke.

For close-range shots, as in skeet, physics dictates that the more pellets you shoot the greater the odds for hitting the target before the smaller (lighter) pellets lose their momentum. So you want to go for a wider choke that lets the smaller, lighter pellets actually swarm around the target while they’re still effective.

Basically, there are three types of chokes.

The fixed choke is already machined into the barrel of the shotgun. You’ll see guns that are designated with skeet chokes, or full and improved cylinder chokes for wingshooting. The type of chokes depends on its specialized use, and will often be accompanied by stock and sight complements.

When you buy a new shotgun, it will include a few screw-in chokes most appropriate for its design. You usually can purchase after-market chokes to fill out your inventory.

Screw in chokes come in two varieties: extended and flush mounted.

Extended chokes protrude above the muzzle and are generally clearly marked; they are designed to be screwed in by hand.

Flush-mounted chokes are screwed entirely into the barrel so that in the end the choke is flush with the muzzle. Newer flush-mounted chokes tend to also be clearly identified. But less expensive or older flush-mounted chokes rely on a notch system to identify their constriction.

Choke Notches
Cylinder /////
Skeet /////
Improved Cylinder ////
Modified ///
Improved Modified //
Full /

Then there’s the adjustable choke. This is a single choke with multiple settings. Turn the selector to set the most appropriate constriction.

Once you have the choke installed, it’s best to pattern it on paper.

You’ll need a pattern target and something disposable to mount it on.

Typically, you’d want to be about 40 yards from your “pattern board.” Draw a 30-inch circle around the center of the pattern and then count the pellets as a means to determine the accuracy of your choke. A full choke should put 70% of its pellets in a 30" circle at 40 yards. A modified choke should put 60% of its pellets in the circle. And an improved cylinder should give you 50%.

Perhaps the biggest risk with chokes is that they become a crutch.

For example, if you consistently missed the #3 station on skeet with a skeet choke, moving to a wider cylinder choke probably won’t help. After all, if you’re on the target, you’re on it. The same can be said of most other clays sports.

Missing shots is generally not a function of your choke selection. It’s a function of your skill, technique and body mechanics.

The worst mistake you can make with a choke is using it as an excuse for missed shots.

If you have a problem station, and you’re using the recommended choke, the best thing you can do is practice, practice, practice.

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Published in Guns