How do you rotate the cylinder of a revolver?

The correct answer focuses on the specific action of manipulating the revolver's internal mechanism. When you pull the hammer back to half-cock, it allows the cylinder to rotate. This position disengages the cylinder from the locking mechanism, enabling it to turn freely to align the next chamber with the barrel for firing. This is a critical operation in revolvers, as it ensures that the firearm is ready for the next shot while maintaining safety.

Employing the other methods mentioned would not effectively rotate the cylinder. Turning the barrel does not directly control the cylinder's position as it is fixed to the frame of the revolver. Using a key lock mechanism is not a standard feature for rotating the cylinder in most revolvers; rather, it might apply to securing the firearm. Manually using fingers to rotate the cylinder may not provide enough leverage and could risk damage or misalignment, as the cylinder is designed to engage with specific internal mechanisms. Thus, manipulating the hammer to the half-cock position is the appropriate and safe method to rotate the cylinder of a revolver.