The documentary series Disney Gallery: The Mandalorian devoted an entire episode to the show’s practical effects and prop work, which included a short explanation from prop master Josh Roth. Since The Mandalorian is pulling almost all of its background context and visual cues from the original trilogy — mostly from A New Hope — Roth explains that when tasked with dreaming up these characteristic weapons, he went back to the roots that George Lucas himself built on, and asked what inspired those original designs. The answer, as the veteran Star Wars fan might expect, is World War II. Production could only afford to rent vintage guns for the first movie, so designs were inherently hampered by the fact no modifications could be too permanent, as the designs were built directly onto the guns. That’s why they sometimes appear bulky or oddly heavy in some shots — they were probably made quite unbalanced by the temporary additions.
For his task, Roth purchased WWII weapons — still very much available on the market in various states of repair — as his reference for illustrating concept weapons, adding stylized modifications on top of the general silhouettes of the real-world guns. Mando’s sidearm looks very much like a German Luger, for example. Decades on and billions of dollars in generated revenue later, it’s a paltry expenditure to mold your own weaponry, but it’s the same conceptual process at work meant to achieve a very specific aesthetic — and, of course, look very cool.