A bunch of the confusion comes when folks that are smokeless, highvelocity type shootes get involved in the low pressure low speed tons of fouling and goo of the blackpowder cartridge world.
You do need to remove the carbon , as there may just be some lead and accumulated blackpowder fouling hidden under that.. Anybody ever heard modern day smokeless shooter whine about barrel pitting in old rifles? Aside from the mercuric priming, stuff hidden under the "carbon" has been setting there slowly etching barrel steel.
Clean up an old "pitted" and dark bore of a rifle from the pre smokeless days, and often a lot of that pitting goes away, but yet you will be bringing out fine rust on the cleaning patches.
I'll bet an owners manual from a VW jetta will work just fine for the Dodge cummins diesel,,, after all they're both diesel engines..
