What tool should be used for hard-to-clean areas on the M9 service pistol receiver area?

Using a soft brush to clean hard-to-reach areas on the M9 service pistol receiver is the best choice due to its effectiveness in dislodging dirt and debris without causing damage. The soft bristles are gentle enough to avoid scratching or marring any surfaces while still being robust enough to clean out accumulated grime in tight spaces. This is particularly important for areas where the pistol's mechanical components meet, as harsh cleaning tools could affect functionality or compromise the integrity of parts.

In contrast, steel wool can be too abrasive and may remove protective coatings or scratch metal surfaces, leading to potential corrosion. Paper towels may not be effective in getting into crevices and can leave lint behind. Compressed air could blow debris further into hard-to-reach areas instead of removing it, complicating the cleaning process.