I know I can't do a muscle pass with coins. I know this as I have tried variously and intermittently for about 6 months. No movement or anything, just sore hands.
While looking through some articles on coin work this evening, I saw a section detailing the muscle pass.
I snorted derisively, and picked up a half dollar to demonstrate that it was impossible. Placed it in classic palm position, and squeezed, just as I had for the last x-hundred attempts.
The coin flew out vertically about 8 inches, surprising the

I tried twenty or so more times, and got varying results, mostly less high, and in some odd directions, but every time I squeezed, the coin moved. This definitely gives me something to build on with the sleight, hopefully I'll be able to get it more under control with more work.
Moral: Try stuff you know you can't do.