The Pressin was a two-shot derringer made to be disguised as a pair of glasses. It was intended for use by politicians, military officers, and other potential victims of kidnapping by groups like the ETA.
It held two rounds of a special 7.65mm E cartridge, which was a rimless .32 ACP with a case cut down to 15mm. It was loaded to a higher pressure than normal .32ACP, firing a 5 gram (77 grain) bullet at 250 m/s (820fps).
Ian’s Video: [11:45] https://youtu.be/FHmFUT9tEdg?si=
Gunpowder produces pressure when burned - it’s very common in gunsmithing to talk about pressures of different cartridges. This is a gunpowder-based weapon