Wounds from Shotguns

Shotguns differ from rifles and handguns in construction, ammunition, ballistics, and use. Rifles and handguns fire a single projectile down a rifled barrel. Shotguns have a smooth bore. Although they can fire a single projectile, they are usually employed to fire multiple pellets. Rifled shotgun barrels, intended for use with slugs, are available. Shotguns may be autoloaders, pump (slide action), over/unders, side-by-side, bolt action or single shot. Some shotguns intended for military and/or police use convert from semiautomatic to pump action and back as the user desires.

Barrel lengths of shotguns range from 18 to 36 inches with 26 and 28 in. the most common. Barrels 18 and 20 in. in length traditionally have been used only for police riot guns. With modern powders, barrel lengths greater than 18 and 20 in. produce only insignificant increases in velocity.1 Longer barrels are really just a matter of tradition, styling, balance, or a desire for a longer sighting radius.

The usual shotgun barrel does not have a rear sight. It possesses only a small rudimentary front sight consisting of a small brass bead. With the increased use of shotguns in deer hunting, manufacturers are now producing shotgun barrels, 20 and 22 in. long, that are equipped with rifle sights as well as optional rifling.

A shotgun barrel is divided into three sections: the chamber, the forcing cone, and the bore.1,2 The chamber is the portion of the barrel that encloses the shotgun shell. It is slightly larger in diameter than the bore. The chambers are cut to the exact full length of the unfold (fired) cartridge case. Between the chamber and the bore, there is a short, tapering section called the forcing cone. This section constricts the charge as it emerges from the shotgun shell, enabling the pellets to be pushed smoothly into the bore.

The archaic term "gauge" is used to describe the caliber of the shotgun.1,2 This term refers to the number of lead balls of the given bore diameter that make up a pound. In 12-gauge for example, it would take 12 of the lead balls to make 1 lb. The only exception to this nomenclature is the .410, which has a bore 0.410 in. in diameter. The actual diameters of the most common gauges are as follows:

Bore Diameter

Gauge

in.

mm

10

0.775

19.3

12

0.729

18.2

16

0.662

16.8

20

0.615

15.7

28

0.550

13.8

.410

0.410

10.2

These are, of course, the nominal bore diameters, as there can be a variation of a few thousands of an inch due to mechanical operations. As the bore size of the shotgun increases, so does the number of pellets that can be loaded in the shot shell. This increase is important to a hunter, as the effectiveness of the shotgun depends on the accumulative effects of several pellets hitting an animal rather than on a single wound by a single pellet. The most popular gauge in the United States is the 12-gauge.

Most shotgun barrels have some degree of "choke," that is, a partial constriction of the bore of a shotgun barrel at its muzzle so as to control shot patterns. The choke may be permanent and built into the barrel or the barrel may accept choke tubes that when screwed in the muzzle determine the choke of the barrel. Choke constricts the diameter of the shot column, increasing its overall length. The outer layers of shot are given inward acceleration as they pass through the area of constriction (the choke). This holds the shot column together for a greater distance as it moves away from the muzzle.

Different degrees of choke will give different spreads for a particular shotgun charge and range. The tighter the choke, the smaller the pattern of pellets. The usual degrees of choke in descending order are full, modified, improved cylinder, and cylinder. The degree of choke is based on the percentage of pellets that will stay inside a 30-in. circle at 40 yd. The only exception to this is the .410 shotgun, in which the pattern of shot is determined at 25 yd in a 20-in circle. In determining the spread of the shot patterns, whether on paper or on the body, one must exclude "fliers," i.e., pellets deformed in the bore that stray from the main pattern.

The following table gives the percentage of shot that can be expected in the various choke borings:

Choke

Percentage at 40 yards in 30-in. circle

Full choke Modified choke Improved cylinder Cylinder

If one examines the table, one sees that a full-choke weapon is supposed to deliver a 65 to 75% pattern.1 In fact, with modern ammunition, it may actually deliver a higher percentage of shot in a 30-in. circle because of improvements in shot shell design. Plastic wads, redesign of composite wads, and plastic envelopes for shot have resulted in an increase in percentage of shot delivered to the 30-in. circle, i.e., "a tighter" grouping of pellets. In a full-choke weapon, large shot sizes such as BB's or #2 shot may give 75 to 85% shot patterns.2 This improvement in pattern performance is true for all chokes. It decreases with small shot sizes, however, so that for a No. 9 shot there is no improvement in patterning. The size of a shot pattern can also be influenced by the brand of ammunition.

In barrels with permanent choke, the chokes may start anywhere from 1 to 6 in. from the end of the barrel. They may end flush with the barrel or 1/2 to 1 in. before it. The amount of constriction, i.e., choke, is relative to the actual bore diameter of the gun, which, as mentioned, may vary a few thousands of an inch. In a 12-gauge shotgun with a 0.725-in. diameter, a full choke barrel has a diameter at the muzzle of approximately 0.694.2

In theory, the cylinder bore has no choke. In practice, however, gun companies put some degree of choke in these barrels because a true cylinder bore throws patterns that are irregular in density and shape and have "holes" in them. Addition of 0.003 to 0.005 in. of constriction will make the pattern round with a more even density of shot.

Unlike rifles or pistols, many shotguns have barrels that are easily removable, so that an individual may have one shotgun but a number of barrels of different choke. Over-and-under and double-barrel shotguns often have a different choke for each barrel. Most shotguns now manufactured accept choke tubes that when screwed into the muzzle of the shotgun barrel change the choke of the barrel. Some older shotguns were equipped with polychokes. These devices were installed at the end of the barrel and permit an individual to go from one choke to another simply by turning a sleeve.

There is one common area of confusion concerning gauge and choke. No matter what the gauge, weapons of identical choke produce approximately the same size patterns at the same range. The pattern will differ only in density. A full-choke barrel, whether 12-gauge or 20-gauge, should put 65 to 75% of the pellets in a 30-in. circle at 40 yd. The only difference is that the 12-gauge shotgun, with its greater number of pellets, will put more of these in the same area. Thus, assuming the same barrel length, choke, pellet size, and range, there should be no difference in the size of the patterns thrown by weapons of different gauges (with the exception of the .410).

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