I agree with Grouch on the cool water ( pour it full, let it sit for 15-20 minutes, dump, repeat, dry, and oil), but not withWD40, unless it is going to be a short time before you go shooting again. Out here on the left coast the WD40 evaporates quickly, and can lead to rusty spots. I prefer BreakFree, or some of the other heavier bodied gun oils.
Hungry Horse