Wild, wonderful world of chokes

Wild, wonderful world of chokes – Shotgunner

Holt Bodinson

What do the following seven shotgun barrel or choke tube designations commonly found on shotguns have in common: 7/10; *-; **; 3/4; 11; .030; IM?

As discerning shotgunners, you probably know, or maybe not, that each one of these seven arcane codes designates a barrel or choke tube with an “Improved Modified” degree of constriction.

Second challenging question. Looking at the muzzle end of a Browning shotgun fitted with Invector Plus choke tubes, what chokes are designated by the following notches cut into the rim of the choke tube: 1; 11; 111; 1111; 1111?

If you’re a dyed-in-the-wool Browning shooter, you probably know that when shooting lead shot, I notch equals Full; 11 notches equal Imp. Mod; III notches equal Mod; 1111 notches equal Imp. Cyl; and 11111 notches equal Skeet choke. However, did you know that when you’re hunkered down in a duck blind shooting steel shot, 11 and 111 notches equal Full; 1111 notches equal Mod.; and 11111 notches equal Cyl. ?

It’s enough to drive you crazy.

Between inch and millimeter measurements, plus historical gunmaking traditions that dictate choke codes, there simply isn’t a common, universal language when it comes to choke designations, and I don’t see any improvements looming on the horizon. So, we do the best we can and keep a few notes tucked away to insure we’re just a little bit knowledgeable when we’re out shopping for a new smoothbore or sounding literate at the range.

As If That Weren’t Enough

I wasn’t going to mention it, but there’s an additional problem when it comes to deciphering the chokes of barrels not fitted with choke tubes. Short of actually measuring the bore and the existing degree of choke constriction, there is simply no way to know what you’re dealing with.

Many fine old doubles have been lightly rebored to remove pits, and many original chokes in shotguns of all makes and ages have been modified by a qualified gunsmith or polished out by the owner using a portable drill and sandpaper wrapped around a dowel.

Remembering that choke is determined and measured as the difference in diameter between the main bore and the tightest portion of the choke, the amount of constriction within the choke will vary depending upon the nominal diameter of the bore. With many modern barrels being overbored, choke tubes for various brands of shotguns will have different degrees of constriction while providing the same degree of choke.

For example, the nominal bore diameter of a 12-gauge Browning shotgun that accepts Invector Plus tubes is 0.742 inches, while that of a Beretta will run only 0.730 inches. Thus an improved modified tube for the Browning might be 0.715 inches while that for a Beretta might be 0.700 inches.

Chokes are described as having a specific degree of constriction. In this regard, both domestic kind foreign makers share a similar set of dimensions, whether they are in inch or millimeter measurements. Here are the standard specifications for chokes expressed in thousandths of an inch:

True Cylinder: 0.000-inch constriction

Skeet-1: 0.005-inch constriction

Improved Cylinder: 0.010-inch constriction

Modified: 0.020-inch constriction

Improved Modified: 0.030-inch constriction

Full: 0.040-inch constriction

Another Country Heard From

On the range, you may often hear the terms “quarter choke” or “half choke” being bandied about. These are the choke designations used in England, and it’s good to know them. They are:

Full: equals Full

IM: equals Three Quarter Choke (3/4)

M: equals Half Choke (1/2)

IC: equals Quarter Choke (1/4)

S-1: equals Improved Cylinder

Cyl: equals True Cylinder

One of the most interesting questions that often comes up when discussing chokes is whether or not a full choked 28 gauge, for example, throws the same pattern as a full choked 12 gauge. The answer is yes and no. Yes, because the diameter of the patterns will be equal at 40 yards. No, because the density of the overall patterns will favor the heavier shot charge delivered by the 12 gauge.

Talking chokes is a fascinating subject. And as knowledge of this subject translates directly to more game harvested in the field, or more clays dusted on the range — we’ll be doing more in the future.

COPYRIGHT 2003 Publishers’ Development Corporation

COPYRIGHT 2002 Gale Group