Which of the following is not a shotgun malfunction?

A foul charge is not categorized as a shotgun malfunction. In the context of shotguns, malfunctions typically refer to issues that prevent the firearm from firing or cycling properly.

Failure to extract occurs when a spent shell casing is not ejected from the chamber after the weapon is fired, leading to a subsequent failure to load a new round. Squib loads refer to an underpowered round that may not generate enough energy to exit the barrel, creating a potentially dangerous blockage. A double feed is when two rounds are attempted to be fed into the chamber simultaneously, causing a jam and preventing the shotgun from functioning properly.

On the other hand, the term "foul charge" does not align with common terms used to describe malfunctions in shotguns. It is important to differentiate between technical malfunctions, which impede the operation of the firearm, and other terms that may relate to ammunition quality or loading issues but do not directly translate to mechanical failures.