Which of the following can cause a misfire in a revolver?

A misfire in a revolver can occur when the primer fails to ignite, which is specifically what happens with a bad primer. The primer is the critical component in the cartridge that ignites the gunpowder when struck by the firing pin. If the primer is defective—whether it's due to moisture, manufacturing defects, or other issues—it will not produce the necessary spark to ignite the powder, leading to a failure to fire. This explains why a bad primer directly causes a misfire.

Other factors can contribute to firing failures but in different contexts. A malfunctioning firing pin might prevent the primer from being struck adequately, while improper ammunition handling could lead to improper seating or damage to cartridges. A cracked barrel generally relates to safety hazards or accuracy issues rather than directly causing a misfire. Thus, the role of the primer is pivotal in understanding why a bad primer is the key reason for a misfire in a revolver.