Throughout the pre-WWI period, Paul Mauser was working continuously to develop a reliable self-loading rifle. Among his many experimental designs was a flapper-locked rifle.
The flapper-locking system was first patented by a Swede named Kjellman, but his design (for a light machine gun) did not get beyond prototype form.
Mauser made a military rifle using the system, and also scaled it down to handgun size as a potential followup to the C96 “Broomhandle” Mauser.
That handgun was designated the 06/08, and used the same basic layout as the C96, with the magazine located in front of the grip. About a hundred were made, and they all used detachable magazines, with examples being made from 6-round to 20-round capacity.
The action was a short-recoil one, locked by a pair of flaps inside the rear.
The flaps would pivot out of contact with the bolt as the action recoiled, and then the bolt would be able to slide back between them (very similar to the Soviet DP/RPD/DShK lone of machine guns, actually).
This example is a gorgeously refinished on, with a 20-round magazine.