The small hole from side to side of the rear of the magazine floorplate cover houses the pivot pin for opening latch.
The two small allen screws that go vertically at the rear, under the plate, hold the replaceable fastener on witch the latch secures.
Seems complex or puzzled because my English is bad, but the mechanism is neat and very sturdy, like a Deeley forend fastener.
The magazine holds five 300HH cartridges.

DORLEAC