How can a 'stovepipe' malfunction occur?

A 'stovepipe' malfunction occurs when a spent casing does not get fully ejected from the firearm after a round is fired. Instead of being sent out of the ejection port, the casing becomes lodged in a vertical position, resembling a stovepipe. This typically happens due to insufficient extraction or ejection forces resulting from issues like a weak extractor spring, a dirty chamber, or other mechanical failures associated with the firearm's operating mechanism.

While the other options describe potential firearms issues, they do not specifically relate to the action of a spent casing getting stuck in a vertical position. For instance, a failure of the bolt to lock correctly can lead to different malfunctions, and a faulty trigger mechanism or an empty magazine will not directly cause the stovepipe issue. Hence, the primary characteristic of the stovepipe malfunction aligns with the incorrect ejection of the spent casing.