Condition means everything when it comes to collecting anything. So when I told my brother that his 81MM mortar shell might fetch him $79 on eBay, it was only because it was in pretty nice condition for one that had been fired sometime back in the late 1960’s (or early 1970’s.) Disassembling it was not so easy. The sealant the Army uses on threads does an excellent job of prevent corrosion, even when both of the mating parts are aluminum. But it may make removal of parts difficult. Heat never works for me, and WD40 is useless because the threads ARE sealed. Brute force then, using improvised tools and means of clamping, even on the aluminum fin section. Photos show removal of fin section and everything else, through improvised means. Ready for eBay!
Many years ago I used to assemble parts such as connectors for military computers. To make sure they never loosen up we applied a thread locker called “Black Max” made by Loctite. You had approx. 30 seconds to complete the process. After that, the connector was on “forever and ever amen”. Nobody was ever able to come up with a way to disassemble it. You just drew out new parts from the crib.
I noticed that two different thread sealers were used on the 81MM I disassembled. The steel to aluminum threads had a blue-colored sealant. The aluminum to aluminum threads used a red-colored sealant. So it sounds like very task specific “Locktite”, with different formulations for different metals. “Lock tight” is what it was, and brute force was necessary.