This is a Bergmann Simplex pistol; you might recognize its forerunner, the Bergmann 1896, as the basis for the Mandalorian's blaster.
This is an early semi-automatic handgun; the front loading cartridge is what gives it that Star-Wars-y profile. The reason is that good Star Wars designs should have stuff on them that definitely goes ka-chunk when you use it. Clear delineation of the Kachunk Zones of a design is an important part of the design process. In anime, its why your mech needs some bits that look like a 🚫 sign, so you know what would go Kachunk if you grabbed it and rotated 45° with your hand.