Couple thoughts: if you look at most factory barrels with a borescope, you will likely wish you hadn't. I've seen some that were so rough, they almost qualified as 'threaded'. Its no wonder they collect fouling like crazy.
If you chose not to clean your barrel after shooting, the powder ash sits in the bore, and collects moisture. Guns treated like that will commonly have a couple inches of severe pitting at the muzzle, from the ash/moisture. If you chose not to clean, you should at least patch out the loose powder fouling. A boresnake would even do that much.