Page "Firearm" Paragraph 8

A problem for firearms is the accumulation of waste products from the partial combustion of propellants, metallic residue from the bullet itself, and small flecks of the cartridge case, collectively known as fouling or gunshot residue.

These waste products can interfere with the internal functions of the firearm.

As a result, regularly used firearms must periodically be partially disassembled, cleaned and lubricated to ensure the firearm's reliability.