Len, as I said over one the AVA, speaking strictly as a layman in terms of technical knowledge, I strongly suspect 2) and 3) are fiction.

The pressure needed to recock the gun after the pellet was expelled at supersonic speed would have to be powder-burner massive, surely?!

And the airgunsmith who can take "one look"? Maybe, but they'd be foolish not to consider the other options too, wouldn't they?!

Or am I just plain wrong?