Actually, both the Michigan laws and the Portland laws or something like them are a lot more common, though not as enforced, perhaps.

A while back when I was still living in Washington State I asked the local DA what the municipal laws and regs were on using a pellet rifle or my red ryder bb gun, or even my wrist rocket. I was told that discharging such items was illegal inside the city limits. Now I don't expect those rules to be enforced unless I do something stupid like shoot someone or get witnessed shooting an animal or someone else's property or otherwise being a nuisance with it. Still, the laws are on the books, so I guess you decide the risks you are going to take. The crime of affray allows someone to file an intimidation complaint against you if they feel you are weilding or or brandishing an item in a threatening manner, and the minimum standard that constitutes a threat gets lower if the item is a weapon of any sort, including a knife, a toy gun, a bb gun, or even a wrist rocket.

Basically, if someone wants to cause you a lot of trouble, it isn't that hard to do. If Mr door to door salesman rings your doorbell and you answer the door with a shotgun in your hand and he sees it, the next visitor to ring you doorbell could be a cop.