Which error commonly leads to Phase II stoppages?

Phase II stoppages typically refer to a specific type of malfunction in firearms, particularly related to semi-automatic pistols. These stoppages usually occur when the firearm fails to feed a new round into the chamber after having fired the previous one, often due to issues with the spent casing or the ejection process.

When considering the options, an obstructed ejection port is a common culprit for Phase II stoppages because it can prevent the spent casing from being properly ejected. If the casing does not exit the firearm, the next round cannot be chambered, resulting in the malfunction. An obstruction may be caused by debris, a malfunctioning component, or even a problem with the ammunition.

This understanding of how an obstructed ejection port can lead directly to a failure in the cycling of the firearm illustrates why this error is linked specifically to Phase II stoppages. Other options may contribute to malfunctions, but they do not directly cause the specific issue of failing to feed a round due to ejection problems.