It's not a mock-up. The select-fire CZ-75 really does exist (see Jane's Infantry Weapons, 1999-2000.) The magazine in front of the trigger guard is attached by means of a shoe in the frame, and is used only as a handgrip. The gun feeds from the normal place, a detachable box magazine inside the handle.
Later,
Chris
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"TV what do I see, tell me who to believe, what's the use of autonomy when a button does it all??" - Incubus, Idiot Box