What factor primarily contributes to a failure-to-eject situation in firearms?

In a failure-to-eject situation, the primary issue involves the fired casing not being fully ejected from the firearm after the round has been fired. This can occur due to several mechanical factors, such as insufficient extractor performance, a dirty chamber, or a lack of proper lubrication. When the casing does not clear the chamber, it remains in the firearm, preventing the next round from loading properly and leading to a malfunction.

The other factors mentioned may contribute to different types of malfunctions. For instance, an incompatible magazine might lead to failure-to-feed issues, while oversized ammunition could create extract problems on its own but wouldn't specifically relate to the ejection cycle. A broken firing pin would primarily cause failure to fire rather than failure to eject. Understanding these distinctions is crucial for diagnosing and resolving issues in firearm operation.