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, fast moving targets with shot.
[1] Under normal circumstances, any firearm with a rifled barrel over 12.7 millimeters (.50 inches) is legally considered a destructive device in the United States.
The short, fat, unaerodynamic Foster slug was no longer needed for its inherent stability; new slugs were smaller in diameter, usually around 10.16 to 12.7 millimeters (.40 to .50 caliber) (compared to the 18.5 millimeter (.73 inch) bore diameter of a 12 gauge), and carried in a plastic sabot.
With the wide selection of barrels, shotshells and slugs, the modern shotgun is a tremendously versatile tool.
While buckshot is capable of taking deer-sized game, it is only effective at short ranges, generally under 50 yards (46 meters).
A properly selected barrel and slug load can increase the range to 150 yards (137 meters) or more.