Which tool is suggested for cleaning the barrel assembly?

Using a cleaning rod with a patch is the most effective method for cleaning the barrel assembly of the M9 service pistol. The design of a cleaning rod allows for better reach and maneuverability within the barrel while ensuring that cleaning patches can effectively remove fouling, debris, and residues that can accumulate after shooting. The cleaning patch, when attached to the rod, ensures that the cleaning solvent or oil can adequately saturate and clean both the rifling and the inner surfaces of the barrel.

This method not only allows for thorough cleaning but also helps in preserving the integrity of the barrel by minimizing the risk of scratches or damage that could occur from less appropriate cleaning tools. Other options such as a sponge or paper towel may not provide the same level of access or cleaning efficacy for the barrel's internal surfaces. A toothbrush, while useful for scrubbing some parts of the pistol, lacks the capability to extend deep into the barrel and clean it effectively, making it less suitable for this specific cleaning task.