I've put the parts into lightly boiling water, that will melt it right off. Don't get the water boiling too rapidly, just barely. Leave them in there for 5-10 mins, take them out and quickly dry, lightly oil everything and should be no rust problems.
This method worked for me on my SKS. I could get everything except the barrel/reciever into the pot of water and it worked good.
Yes, that's what I did on my SKS small parts. It gets all the cosmo gunk
out of the trigger group and the other nooks and crannies.
I had to scrub the pan a couple of times before it was ready to go back
in the cabinet.