Bottom Line: Coins (and shells) are MOODY.

That's why Bang Rings were invented...

It's 'Hammer Time'...

Thanks ...I tried the ice cube method ...worked like a charm.

This happened to me yesterday, and here's what worked...I don't know which steps contributed, and if going straight to the last step would have worked.

1) Heated the shell/insert with a hair dryer on "hot".
2) Placed ice cubes on each coin face, and placed in freezer for 30 minutes.
3) With the ice cubes stuck to each face, I tried to separate the coin & shell. Coin would spin in the shell, but not separate.
4) While still very cold, applied heat from hair dryer to shell. Still, would not separate if banged against my hand.
5) Placed the stuck coins into a small plastic cup used to measure coffee beans. Gently shook the cup twice, and the coins separated.

The shell was not damaged in the process.

Another thing I have heard that can be used in hot glue sticks. Heat one end of a stick up and firmly press it onto one side of a jammed gimmick. Then do the same for the other side. Once the glue sticks are bonded, pull in opposite directions. Of course, do this method over carpet! But, the glue should not heat enough to discolor the coins, nor should it leave residue like duct tape might.