It's your face that you're putting next to the rifle. You get to decide how much risk of boom you want to take.
Me personally, I clean the barrel and bolt face. The rest only as needed.
Meh, I've literally shot cosmoline out of an SKS barrel. It wasn't completely plugged with the stuff, I could see some light through it, but there was an awful lot. I wanted to see what would happen and the answer was nothing. It shot fine and continues to.