Just took delivery of an Ishapore .308. Just came in the mail! (UPS)
R Lee is getting impatient with you son.

Sorry Haz, I posted this from your first post so I did not see your answer, Mineral spirits works great on cosmoline but you will need some scrub brushes, Best If you can come up with say a 55 gallon drum cut in half, like for a BBQ put in about 5 gallons of mineral spirit, disassemble rifle let it soak for a while then scrub the crap out of it.
We used to use warm gasoline, that was tricky, and interesting

Oh, remember, Mineral spirits will remove the stock finish as well.