The term 'gun barrel cleaner' refers to a tool used to clean the inside of a gun barrel. The two crossword solutions for this term are 'SWAB' and 'RAMROD'. A SWAB is a piece of cloth or sponge attached to a handle, which is used to clean the inside of a gun barrel. A RAMROD is a long, thin rod used to push a cleaning patch through the barrel of a gun. Both of these tools are essential for cleaning a gun barrel and ensuring that it is free from dirt and debris.