Foster type rifled slugs
The eventual solution to this problem was the Foster "rifled" slug. This is a short, blunt lead bullet that is solid in front and hollow in the rear, analogous to a badminton bird. And, like a shuttlecock, it is its weight forward balance that allows the Foster slug to fly through the air to its target with reasonable accuracy. Compared to lead balls, this was a big improvement in both accuracy and SD.
Heavy external "rifling" was cast into these Foster type slugs, allegedly to allow the air they flew through to impart a slow spin that would help stabilize the slug. Like most something for nothing schemes, the rifling proved ineffective, but it did provide some space for some compression if the slug had to squeeze through a tight choke. The name "rifled slug" stuck and is still in widespread use today.
Rifled slugs are offered by most of the major ammunition makers in a variety of shotgun gauges, including 12, 16, 20, and .410 bore. They used to be made under bore diameter to allow safe passage through any degree of choke, from full to cylinder. Cylinder bore guns are usually recommended for shooting slugs, but in some cases a full or modified choke barrel will give better accuracy with the undersize slugs.
This may not always hold true these days, however, as Remington advertises that their "Slugger" rifled slugs are made oversize for better sealing against the barrel wall and superior accuracy. Compared to rifle bullets, whose diameter is held to very strict tolerances, Foster type slugs are made to rather haphazard dimensions that vary from one manufacturer to another.
