rifled slug

A combination gun is a firearm that comprises at least one rifled barrel and one smoothbore barrel, that is typically used with shot or some types of shotgun slug. Most have been break-action guns, although there have been other designs as well. Combination guns using one rifled and one smoothbore barrel usually are in an over and under configuration. Side-by-side versions are referred to as cape guns.
A drilling (German for "triplet") is a combination gun that has three barrels. A vierling (German for "quadruplet") has four barrels. Combination guns generally use rimmed cartridges, as rimless cartridges are more difficult to extract from a break-action weapon.

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