I'm like every armorer I know, I HATE Cosmoline!
But it DOES work because it's so hard to penetrate and it gets into EVERY nook, cracks and crannies...
REALLY hard to get out unless you boil the darn firearm to get it out, and boiling takes effort, makes a mess and generally ruins your day (Or Days, depending on how many you are un-crating).
If you need to break something loose,
There is NOTHING LIKE KANO AREOKROIL!
Been a machinist, gunsmith/armorer, welder, farmer for most of my life, about 40 years, and I've never seen ANYTHING like this stuff!
Expensive, but goes a long way, and it simply WORKS when nothing else will!
Link: Link Removed
At around $10 a can, you REALLY don't want to be using it for a job WD-40 or PB Blaster will work,
But if you have something REALLY STUCK, this is the ticket!
I recently had a full length hinge on a trailer door that hadn't opened in about 4 years, so it was rusted SOLID,
Been soaking it with WD-40 for over two weeks, two or three times a day and trying to work that hinge enough it wouldn't bend the frame...
One does of AreoKroil and 20 minutes later it was working, two more doses and it worked like new!
Just to see if it was a fluke, I dosed the hinge on the other side of the storage/tool box that hadn't had anything done to it (Worse shape than the first, and I 'KNEW' I was going to need replaced),
Turned out in 30 minutes the Areokroil had knocked it loose!
Two or three more doses and it was working like new!
Just knocked loose the bolt in a Bren Gun that had been stored unprotected in a basement since the owner got sick (Very old),
One afternoon soaking in Areokroil and it works like new...
Still needs a good cleaning, but it cycles and cycles SMOOTH!