This is an extremely rare pistol that was produced in very limited numbers and commonly referred to as the Schwarzlose "toggle-top" pistol by collectors.
The Schwarzlose M-1900 was never put this pistol into production and it is estimated that only a very few prototype pistols were actually manufactured, so that the company had a working design to use for filing the patent. This design was patented under British Patent 6056/1900. It is assumed that this pistol was manufactured only to protect the action design.
This pivot pin/toggle joint design was later used in the Schwarzlose machine gun which was a standard issue firearm in the Austro-Hungarian Army throughout World War I.
The design uses a delayed-blowback type mechanism (where the breechblock is not locked) where the pivot pin/toggle joint is positioned above breechblock and frame. So when the pistol is fired, the complete toggle mechanism raises up to extract the spent cartridge and then closes, strips a round from the magazine and sits on top of the receiver.
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