What type of brush is commonly used for cleaning the bolt carrier group?

A stiff nylon brush is commonly used for cleaning the bolt carrier group because it effectively removes carbon buildup and debris without damaging the surfaces of the components. The bolt carrier group is a critical part of the firearm, and using a brush that is too stiff or made of metal could scratch or wear down the finish, potentially leading to operational issues.

The stiffness of the nylon bristles allows for thorough cleaning while being gentle enough to protect the integrity of the bolt carrier group. Additionally, nylon brushes are resistant to chemicals typically used in cleaning solvents, making them suitable for this application. This ensures that they maintain their shape and effectiveness over time, providing consistent and reliable cleaning performance.