The primers contain potassium chlorate. This deflagrates into potassium chloride, a salt. Being a salt, it is hygroscopic (attracts moisture).
What will remove table salt from a surface? Pure water, right?
Reckon Hoppes might remove it too?
Here's the thing: Lots of folks swear by soap and water. Problem being, soap is hygroscopic as well and a bunch of Dawn down the tube will rust it out surely as any salt.
When I shot corrosively-primed ammo, before I began to handload for this cartridge, I would make up some dishwater and dip ONE patch in it. I'd follow that by four or five tepid-water-soaked patches to make sure the soap was clear.
I'd then clean as normal.
I shoot out back. If you have to go to a range, just do this... and it's the same as I'd do now: Run a patch full of Hoppes or CLP or whatever down the barrel and let it soak on the drive home. The petroleum-based products won't let the metal oxidize even if it weren't cleaning it out!
Think about this: I shoot black powder. If I recall correctly, the residue is actually slightly corrosive, bonding with O2 and forming a weak acidic solution.
The best cleaning for those is just tepid, soapy water pumped through the barrel. Let dry and run some organic grease down the tube. (I use beeswax.)
A lot of folks get so uptight about a few salts that they don't stop to think about how this was handled back in the days of black powder and corrosive primers.
Usually they were just washed out in a convenient creek.