If you full-length size cases during reloading this will eventually happen to you: You’ll run a case into the sizing die and then rip the rim off trying to extract it. At this point you’ve stuck the case in the die and normally you have a long ordeal ahead of you to get it out so you can keep reloading. Some poeple don’t even bother trying and instead send the die back to the manufacturer to get the stuck case removed.
I’ve never been able to free a stuck case with penetrating lubricants: Evidently the brass forms a very tight seal with the die. You can buy or improvise a “stuck case remover” system consisting of a drill, tap, screw, and standoff washer. With a lot of work you can tap the case head and use a fine-threaded screw to slowly pull it out. I’ve done that.
Then I came up with the following trick:
It takes advantage of brass’s high thermal conductivity and the fact that metals shrink when cooled. By spritzing the exposed brass with super-evaporative coolant — the trifluoroethane that sprays out of an inverted dust-off can is convenient — the brass will quickly shrink and separate from the die. You then have a moment to either hammer or screw it out with the die’s decapping rod.
Note that you can only hammer it out if the die allows you to unscrew the rod from the die body. In this case don’t take the locking bolts all the way off the rod though, since hammering may mushroom the top of the rod enough that you’d have to grind it to get the locking bolts back on. If you’re going to screw the rod in to push the case out then take the locking bolt off and before spraying the case have the rod screwed into the web of the case head so it’s ready to push.