Law Level Six
Everything's banned except stunners and shotguns.
Stunners are reasonable, though not necessarily proportional, force.
With shotguns, I think the real issue that regime would have would be with concealability, capacity, rate of fire, and possibly destructiveness.
That means that there would be a minimum barrel length, and a minimum total length, perhaps disqualifying folding stocks.
Capacity is harder to control with semi automatics, lever action, and pump action, since you could extend tubes and possibly add an external magazine; you could be limited to two shells, plus one chambered, which I always thought gave a tri barrelled shotgun leeway.
I've seen people reload remarkably fast, through practice and gimmicks, so this may be less of a handicap than conceived.
You might need to take down a rhino equivalent, or whatever kaiju can tow a spaceship, but I suspect twenty millimetre calibre would probably be the limit.
Non residents and transients may still need to obtain permits and undergo background checks, though in an interstellar civilization, this may not be exactly viable, and subject to forgery, fraud or identity theft; this may be supplemented with a monetary bond, and possibly a personal bond from a local resident.