ORIGINAL: shamlin
Im not sure about a shotgun. When I was in the Marines they taught us that a dirty bore would cause a rifle to be less acurate.
There are worse things that could happen..... Carbon built up is flamable, not something you want around when the gun is fired, not to mention if the action isnt clean it will have trouble loading (pump, or auto) shells. (jams).
Thats certainly true of high volume of fire weapons such as you devil dogs use. On hunting rifles, I use a practice that not a lot of folks do... once I have my rifle dialed in before the season.... I don't clean the bore at all until after the season is over, save perhaps a dry patch to remove debris. Rationale there of course is that any oil in your bore at all will cause you to shoot to a differnet point of impact. So you either need to sight in ALWAYS with a clean barrel... or hunt with a dirty one.