Which condition may prevent the fore-end/slide of a shotgun from closing fully?

A jammed or bent shell stop can prevent the fore-end or slide of a shotgun from closing fully because the shell stop is a critical component that controls the movement of the ammunition as it feeds into the chamber. When the shotgun is operated, the fore-end must move backward and forward to eject the spent shell and chamber a new one. If the shell stop is jammed or bent, it can obstruct the free movement of the shells into the chamber, thus preventing the fore-end from completing its cycle and fully closing. This creates a mechanical failure that can interfere with the function of the shotgun.

In contrast, a dirty barrel may affect the performance of the shotgun but is unlikely to create a mechanical blockage in the fore-end movement. A dislocated front sight impacts aiming rather than the mechanical operation of the shotgun, and a misaligned stock affects comfort and shooting posture but does not interfere with the action of the slide or fore-end closing.