A slug barrel
is a barrel for a shotgun
that is designed primarily to fire slugs
When slugs are fired in a standard, choked
barrel, the slug is deformed by the choke as it exits. The degree of deformation is most acute with fuller chokes, which were among the most widely used in stock shotguns up until about 1990. Early shotgun slugs were "rifled" with deformable fins cast into the outside of the soft lead
slug, which allowed the slug to swage
down to fit the choke. With an open choke, the reduction in diameter is minimal, so accuracy does not suffer much; tighter chokes, however, deform the slug enough to impact accuracy significantly, and the impact of the slug on the choke (at velocities around 450 meters per second (1500 feet per second)) could also stretch the barrel with repeated firings.
The first slug barrels
The first slug barrels were cylinder bore barrels (no choke) outfitted with rifle
sights, which are far better suited to accurate shooting of still targets than the standard bead sight used for shooting small, moving targets with shotshells
. Most pump-action
and semi-automatic shotguns
have barrels that can easily be changed in under a minute without tools, so having more than one barrel for a single shotgun is common. With the addition of a slug barrel, the standard shotgun used for bird hunting
or trap shooting
can then be used for hunting large game, such as deer
at ranges of over 100 meters (100 yards).
Rifled choke tubes
A later innovation was the rifled
choke tube. It could be used in any barrel designed to use interchangeable choke tubes, and it provided rifling for the last few inches of the shotgun barrel. While this wasn't enough to impart a large amount of spin, it did impart some, and that was all that was needed for the short, fat, and inherently stable shotgun slugs of the time.
The rifled slug barrel
The next step was the "Paradox" barrel by Hastings, a manufacturer of aftermarket rifled slug barrels. The term "paradox" had been used in the late 19th century to describe large bore guns with the last several inches of the barrel rifled, similar to a rifled choke tube. The name was chosen because shotguns are defined by their smoothbore barrels, and a "rifled shotgun" was something of a contradiction in terms--not to mention a tricky legal issue, as any firearm
with a rifled barrel over 12.7 millimeters (.50 inches) is legally considered a destructive device in the United States. A BATFE
ruling was obtained stating that a firearm designed to fire shotshells
that was converted to fire shotgun slugs
with the addition of a rifled barrel was still a shotgun, and thus not a destructive device. Now many manufacturers offer shotguns for sale with rifled barrels already installed. Bolt action
and single shot break-open designs are particularly accurate, and with modern saboted
slugs designed for use only with rifled barrels, the modern slug gun offers nearly the accuracy of a typical rifle
New slug technology
The widespread availability of rifled shotgun barrels was quickly followed by the introduction of special slugs designed for use with the rifled barrels. The short, fat, unaerodynamic Foster slug
was no longer needed for its inherent stability; new slugs were smaller in diameter, usually 12.7 millimeter (.50 caliber) (compared to the 18.5 millimeter (.73 inch) bore diameter of a 12 gauge), and carried in a plastic sabot
. The saboted slug had half the frontal area of the old slugs, which translated to half the drag, and double the penetration
. Lighter, faster
slugs were also possible, allowing for a flatter trajectory and longer range. With the wide selection of barrels, shotshells and slugs, the modern shotgun is a tremendously versatile tool.
Shotgun slugs for safety
While shotgun slugs were originally developed as a convenience to the hunter who already owned a shotgun and did not want to purchase a rifle for hunting game
, heavily populated areas now allow large game hunting only
with shotguns. The limited range of the slow, fat slug--even a saboted slug--compared to a rifle bullet offers a safety advantage by limiting the maximum range. While buckshot
is capable of taking deer-sized game, it is only effective at short ranges, generally under 50 meters (50 yards). A properly selected barrel and slug load can triple that range.