45 pistols tend to collect residue on the slide near the muzzle. Some guns may collect this on the barrel near the muzzle. Revolvers collect this in the cylinder and breech area. Residue is gritty like sand. I fear wiping over this reside with the cloth may scratch or dull the gun's finish over time. This is why when cars are washed, they should first be thoroughly rinsed with water pressure to loosen and float off any abrasive grit before any brushes or scrubbers are used on the paint.