I have only used the wd 40 method, works great. Then heavy cleaning/lub.
I dont like using water, on my metals. Just never did that.
Acetone works very well. Or soak parts in hot soapy water.
I've used HOT soapy water and a stiff brush and lots of rags. Water needs to be scalding, so it evaporates quickly. strip the gun, dump in all parts to be cleaned, grit your teeth and start scrubbing. Most of the cosmo will just soak off in the water. Make sure you dry thoroughly and lube well.