Unlike rifle barrels that are sized according to calibers, shotgun barrels are designated by "gauges," the measurement of the inside diameter of the barrel. The rule of thumb is that the larger the number of the gauge, the smaller the diameter of the shotgun barrel's bore. Conversely, the smaller the gauge number, the larger the bore's actual size. Sound confusing? It won't be once you understand the history behind how gauge sizes are determined.
The original method of measuring a barrel's gauge was to fashion lead balls with diameters equal to that of the shotgun barrel's bore size. The total number lead balls of a particular size equal to a pound in weight gives the "gauge."
For example, 12 balls per pound equals a 12 gauge. The 20 gauge shotgun means 20 lead balls equal in size to the gun's barrel diameter constitute one pound. Therefore, the 12 gauge is larger in bore size than the 20 gauge.The most common shotgun gauges in use today are: the 10, 12, 16, 20, and the 28. The very narrow .410 bore shotgun is not a gauge at all. It is actually a caliber, that is, a bore diameter size measured in inches.
The shorter barrel is employed where a quick mount is needed, particularly when hunting upland game, wild turkey or even big game such as deer.
A shotgun's "choke" indicates the degree of internal constriction located at the muzzle end of the barrel. When a shotgun is fired, the shotshell breaks apart and the individual shot pellets are ejected. As the pellets travel, they spread out (the further the distance, the wider the spread); this is known as the shot pattern or spread. Chokes are used to control the shot pattern.
Just as when the nozzle constricts water flow and a narrow, more powerful stream is produced, the narrower the choke the tighter and more distant the shot pattern flies after it exits the barrel. Open the nozzle and the water stream widens to a spray. Open the choke and the shot pattern also begins to spread out.
Most modern shotguns come with interchangeable screw-in choke tubes that allow quick choke changes to meet the demands of match or field conditions. Older models were more likely to have "fixed" chokes requiring several different barrels, each with a different choke.
The three most common choke types are "full" (tightest constriction forcing a narrow, dense shot dispersion, delivering about 70% of the shell's pellets in a 30" circle at 40 yards); "modified" (less constricted with a medium-wide pattern, A barrel lacking any sort of choke is called "cylinder bore" and delivers the widest possible shot pattern, placing approximately 40% of the pellets in the patterning circle at 40 yards. Specialty chokes such as the skeet choke is designed to put 50% of the shell's pellet in the patterning circle at 25 yards.
Note: Steel shot can be used in improved cylinder and modified cylinder choke tubes. However, never use steel shot in a fixed full choke or any full chokes tube unless it is marked specifically "lead or steel." To do otherwise can damage the barrel.
Unlike rifles and handguns, shotguns are "pointed" rather than sighted at the target. For this reason, and also because shotguns deliver a screen of pellets toward a target rather than a single bullet, sights are not quite as important as when aiming a rifle.
The most commonly used sight on a shotgun is in the form of a bead placed at the end of the barrel above the muzzle. Some have a second bead near the center of the barrel to aid quick alignment.
Telescopic sights are available to the hunter for use with slugs or buckshot against deer, or pellets against wild turkey.
Types of Shotguns
There are three basic types of hinged or break action shotguns: the single shot, the over-and-under, and the side-by-side. Each name describes the actual configuration of the three shotgun types. The single shot has only one barrel and holds only one shell at a time. The over-and-under has two barrels stacked one on top of the other. The side-by-side's barrels are beside each other on a single horizontal plane.
Note: there are other hinged or break action variations that include a rifle caliber barrel. For example, one popular variation has a single shotgun barrel located directly under a rifled barrel. Another variant, popular in Pre-World War II Germany, is called a drilling and has two shotgun barrels arranged in a side-by-side configuration with a rifled third barrel affixed beneath the two smooth bore tubes.
Shotgun shells, just as shotguns themselves, are classified by gauge (10, 12, 16, 20, 28 and .410 bore). And just as with handgun and rifle ammunition, accidentally loading the wrong size shotgun shell into a particular chamber can have explosive and dangerous consequences.
A 20 or 28 gauge shell mistakenly placed into a 12-gauge gun can become lodged in the barrel. Firing a subsequent 12 gauge shell behind it will cause potentially lethal fireworks and shrapnel.
Shotshells are manufactured in lengths to fit the chambers of specific shotguns (2-3/4 inches, 3 inches, 3-1/2 inches). The longer the shotshell, the more shot pellets it can contain.
The amount of gunpowder used in shotgun shells is described in terms of dram equivalents, a measure of the velocity generated by that particular charge. Black powder charges were measured in drams. So a dram equivalent of modern smokeless powder (example: 2-1/2 dram equivalents) used to propel a particular amount of shot is equal in velocity to 2-1/2 drams of black powder loaded behind the same number of pellets. The key point to remember when comparing shotgun ammunition is that the larger the dram equivalent, the more powerful the powder charge and the higher the velocity of the particular load.
Given the concern about lead being introduced into the atmosphere, Federal regulations for waterfowl hunting now dictate the use of non-lead shot. As a result, a variety of non-lead shot is available, including steel, bismuth, and alloys such as tungsten steel, tungsten iron and tungsten polymer.
Steel shot, in general, has a higher velocity when it first exits the muzzle than does lead. Because it is less dense (lighter) than lead, steel shot loses its ability to "knockdown" game at longer distances. However, the use of larger steel shot sizes can maintain a velocity and retained energy comparable to that of lead, even over a long distance. Many ammunition makers offer the rule of thumb that in order to achieve velocity and retained energy equal to lead pellets, use steel shot two sizes larger than you would for lead.
Shot pellets in modern shotgun shells, are often loaded in flexible polyethylene plastic shot cups that seal the powder's gases for maximum performance.
Shot sizes range from the smallest No. 9 that is .08 inches in diameter to 000 buckshot (call it "triple ought buck" if you want to sound like an old-timer) that is .36 inches in diameter or approximately the same size as a .38 special or 9mm handgun bullet.
With the federal requirement for non-lead pellets, new shot sizes were introduced to compensate for lighter, less dense metals such as steel. These are larger pellets classified as BBB (.19 inches), T (.20 inches) and TT (.210 inches).
The amount of shot in an individual shotgun shell is measured by weight in ounces for all but the large steel and buckshot sizes. They are measured by the number of pellets per shell, or shot charge. To give you an idea of how the number of pellets per ounce varies
Pellets are not the only projectiles fired from shotguns. Slugs are essentially large lead "bullets" used for deer hunting in jurisdictions that prohibit rifles. Some have rifled indentations around them for better stability in flight. They are also used by the military and law enforcement.
Another variation is the "saboted" slug. A sabot (pronounced "saa-bow," from the French word for wooden shoe) could be described as a "shoe" into which the projectile fits prior to being fired. In the days of black powder and muzzleloaders, a saboted projectile was one that had a wooden or metal "shoe" fitted around it to make it better fit the rifling of the cannon or firearm barrel. Today, the sabot is typically made of a plastic-like substance that temporarily enlarges the diameter of the "bullet" for a more snug fit in the barrel's bore. After leaving the muzzle, the sabot falls away leaving the smaller projectile speeding towards its target. The saboted slug may be made of brass or lead and travels quite accurately to an effective range of 100 yards.Slugs should always be used in a cylinder bore barrel, and not in a barrel with a constricted choke.
When you are hunting, the combination of shot size, powder charge, and choke are important. The game loads required to bring down game quickly and efficiently differ from clay target loads. Be sure to check whether you are buying target or game loads depending on your intended use.