Shotgun slug
A shotgun slug is a heavy projectile made of lead, copper, or other material and fired from a shotgun. Slugs are designed for hunting large game, and other uses, particularly in areas near human population where their short range and slow speed helps increase safety margin. The first effective modern shotgun slug was introduced by Wilhelm Brenneke in 1898, and his design remains in use today. Most shotgun slugs are designed to be fired through a cylinder bore, improved cylinder choke, rifled choke tubes, or fully rifled bores. Slugs differ from round ball lead projectiles in that they are stabilized in some manner.
In the early development of firearms for the year 1875, smooth-bored barrels were not differentiated to fire either single or multiple projectiles. Single projectiles were used for larger game and warfare, though shot could be loaded as needed for small game, birds, and activities such as trench clearing and hunting. As firearms became specialized and differentiated, shotguns were still able to fire round balls, though rifled muskets were far more accurate and effective. Modern slugs emerged as a way of improving on the accuracy of round balls. Early slugs were heavier in front than in the rear, similar to a Minié ball, to provide aerodynamic stabilization. Rifled barrels, rifled slugs and rifled choke tubes were developed later to provide gyroscopic spin stabilization in place of or in addition to aerodynamic stabilization. Some of these slugs are saboted sub-caliber projectiles, resulting in greatly improved external ballistics performance.
A shotgun slug typically has more physical mass than a rifle bullet. For example, the lightest common.30-06 Springfield rifle bullet weighs 150 grains, while the lightest common 12 gauge shotgun slug weighs oz. Slugs made of low-density material, such as rubber, are available as less than lethal specialty ammunition.
Uses
Shotgun slugs are used to hunt medium to large game at short ranges by firing a single large projectile rather than a large number of smaller ones. In many populated areas, hunters are restricted to shotguns even for medium to large game, such as deer and elk, due to concerns about the range of modern rifle bullets. In such cases a slug will provide a longer range than a load of buckshot, which traditionally was used at ranges up to approximately, without approaching the range of a rifle. In Alaska, seasoned professional guides and wild life officials use pump-action 12 gauge shotguns loaded with slugs for defense against both black and brown bears under.Law enforcement officers are frequently equipped with shotguns. In contrast to traditional buckshot, slugs offer benefits of accuracy, range, and increased wounding potential at longer ranges while avoiding stray pellets that could injure bystanders or damage property. Further, a shotgun allows selecting a desired shell to meet the need in a variety of situations. Examples include a less-lethal cartridge in the form of a bean bag round or other less lethal buckshot and slugs. A traditional rifle would offer greater range and accuracy than slugs, but without the variety of ammunition choices and versatility.
Design considerations
The mass of a shotgun slug is kept within SAAMI pressure limits for shot loads in any given shotgun shell load design. Slugs are designed to pass safely through open chokes and should never be fired through tight or unknown barrels. The internal pressure of the shotshell load will actually be slightly higher than the equivalent mass slug projectile load, due to an increased resistance that occurs from a phenomenon known as shot setback. Common 12 gauge slug masses are oz (, 1 oz (, and oz (, the same weight as common birdshot payloads.Comparisons with rifle bullets
A 1 oz. A slug also becomes increasingly inaccurate with distance; out to or more, with a maximum practical range of approximately. In contrast, centerfire cartridges fired from rifles can easily travel at longer ranges of or more. Shotgun slugs are best suited for use over shorter ranges.Taylor knock-out factor
The Taylor knock-out factor was developed as a measure of stopping power for hunting game, however it is a rather flawed calculation. It is defined as the product of bullet mass, velocity and diameter, using the imperial units grains, feet per second and inches :Some TKOF example values for shotgun slugs are:
To compare with rifles, some TKOF example values for rifle cartridges are:
Types
Full-bore slugs
Full-bore slugs such as the Brenneke and Foster designs use a spin-stabilization method of stabilization through the use of angled fins on the slug’s outer walls. The slight 750 RPM spin is enough to stabilize the slug because the slug’s center of pressure is so much further back than its center of mass. Saboted slugs are similar in shape to handgun bullets and airguns pellets. Their center of pressure is in front of their center of mass, meaning a higher twist rate is required to achieve proper stabilization. Most saboted slugs are designed for rifled shotgun barrels and are stabilized through gyroscopic forces from their spin.Brenneke slugs
The Brenneke slug was developed by the German gun and ammunition designer Wilhelm Brenneke in 1898. The original Brenneke slug is a solid lead slug with ribs cast onto the outside, much like a rifled Foster slug. There is a plastic, felt or cellulose fiber wad attached to the base that remains attached after firing. This wad serves as a gas seal, preventing the gasses from going around the projectile. The lead "ribs" that are used for inducing spin also swage through any choked bore from improved cylinder to full. The soft metal, typically lead, fins squish or swage down in size to fit through the choke to allow for an easy passage.Foster slugs
The "Foster slug", invented by Karl M. Foster in 1931, and patented in 1947, is a type of shotgun slug designed to be fired through a smoothbore shotgun barrel, even though it commonly labeled as a "rifled" slug. A rifled slug is for smooth bores and a sabot slug is for rifled barrels.Most Foster slugs also have "rifling", which consists of ribs on the outside of the slug. Like the Brenneke, these ribs impart a rotation on the slug to correct for manufacturing irregularities, thus improving precision. Similar to traditional rifling, the rotation of the slug imparts gyroscopic stabilization.
Saboted slugs
Saboted slugs are shotgun projectiles smaller than the bore of the shotgun and supported by a plastic sabot. The sabot is traditionally designed to engage the rifling in a rifled shotgun barrel and impart a ballistic spin onto the projectile. This differentiates them from traditional slugs, which are not designed to benefit from a rifled barrel. Due to the fact that they do not contact the bore, they can be made from a variety of materials including lead, copper, brass, or steel. Saboted slugs can vary in shape, but are typically bullet-shaped for increased ballistic coefficient and greater range. The sabot is generally plastic and serves to seal the bore and keep the slug centered in the barrel while it rotates with the rifling. The sabot separates from the slug after it departs the muzzle. Saboted slugs fired from rifled bores are superior in accuracy over any smooth-bored slug options with accuracy approaching that of low-velocity rifle calibers.Wad slugs
A modern variant between the Foster slug and the sabot slug is the wad slug. This is a type of shotgun slug designed to be fired through a smoothbore shotgun barrel. Like the traditional Foster slug, a deep hollow is located in the rear of this slug, which serves to retain the center of mass near the front tip of the slug much like the Foster slug. However, unlike the Foster slug, a wad slug additionally has a key or web wall molded across the deep hollow, spanning the hollow, which serves to increase the structural integrity of the slug while also reducing the amount of expansion of the slug when fired, reducing the stress on the shot wad in which it rides down a barrel. Also, unlike Foster slugs that have thin fins on the outside of the slug, much like those on the Brenneke, the wad slug is shaped with an ogive or bullet shape, with a smooth outer surface. The wad slug is loaded using a standard shotshell wad, which acts like a sabot. The diameter of the wad slug is slightly less than the nominal bore diameter, being around for a 12-gauge wad slug, and a wad slug is generally cast solely from pure lead, necessary for increasing safety if the slug is ever fired through a choked shotgun. Common 12 gauge slug masses are oz, 1 oz, and oz, the same as common birdshot payloads. Depending on the specific stack-up, a card wad is also sometimes located between the slug and the shotshell wad, depending largely on which hull is specified, with the primary intended purpose of improving fold crimps on the loaded wad slug shell that serves to regulate fired shotshell pressures and improve accuracy.It is also possible to fire a wad slug through rifled slug barrels, and, unlike with the Foster slug where lead fouling is often a problem, a wad slug typically causes no significant leading, being nested inside a traditional shotshell wad functioning as a sabot as it travels down the shotgun barrel.
Accuracy of wad slugs falls off quickly at ranges beyond, thereby largely equaling the ranges possible with Foster slugs, while still not reaching the ranges possible with traditional sabot slugs using thicker-walled sabots.
Unlike the Foster slug which is traditionally roll-crimped, the wad slug is fold-crimped. Because of this important difference, and because it uses standard shotshell wads, a wad slug can easily be reloaded using any standard modern shotshell reloading press without requiring specialized roll-crimp tools.