Text copied from old manual :

The MVM is a newly developed Soviet fuze.
It was designed primarily to be used in antitank mines to be laid by mechanical means and mines which are to be transported while armed.
Basically this fuze consists of a metal case, a diaphragm, a spring loaded, ball retaining striker, and a safety pin.
The safety pin is inserted through the top of the case and striker shaft.
Pressure on the cover breaks the diaphragm, forcing the cap down.
The cap moves down until a recess in the side is opposite the striker retaining ball.
The ball then escapes into the recess and releases the spring loaded striker against the percussion cap, starting the firing chain.