One thing I may add though is its usually quite dry in edmonton humidity wise, that may have helped play a roll as its not sucking up moisture and allowing the salts to work.
I can vouche for this.
I thought I cleaned my 858 when I got back from the range after about 200 rounds of corrosive. I oiled and everything.
1 week later. Rust Ahoy!
There was some rust on inside of the reciever and quite a bit on the bolt face.
So I stripped it down past the bolt and scrubbed with a copper brush/steel wool and drowned it in oil. The rust cleaned up quite well and there was no pitting. Bore is still pristine. Also like others have said, how did you get your piston so clean?
My Ruskie SKS on the other hand is a champ. No rust at all. Even with a lazy cleaning. But she too got pampered and scrubbed out real good. Bore is mirror shiny.
The humidity is quite bad in the basement so I set up the dehumidier on continuos run, blasting the gun storage area with dry desert air. That looks like it did the trick altough at the same time it looks like the oil evaporates faster.




















































