Have you ever tried flooding it with solvent and letting it sit for a bit before hosing it out with HOT water? We used to clean our M16's like that and it worked great, I clean all my semi auto's in the sink and when I get a bunch of grunge in any other gun it gets sink treatment too. The thing to be careful of is that you use hot enough water that it will evaporate out of the action and/or hose it out with some kind of solvent or oil afterwards.