Every time you fire your gun, carbon, lead, copper and plastic—if shooting shotgun—residue are left in the barrel, chamber and action. Fouling built up over time can impact a gun’s reliability. A gunsmith told me his gun cleaning routine depends on the gun. After every use, he cleans his precision rifle. However, he rarely cleans his .22s. Copper build up inside a gun’s barrel can effect the bullets velocity by slowing it down. Further, barrel fouling also affects the barrel’s rifling. Shooting a dirty precision rifle can greatly effect the gun’s accuracy.