They can pass laws, but who’s going to enforce them?
The local police force will enforce these laws of course.
Front-line officers may grumble, but anyone who refuses an order will be fired and there will be no shortage of replacements.
Enforcement will be sporadic and capricious. They won't go house-to-house, but a traffic stop involving a CCW permit holder will likely escalate into an arrest for "transport of loaded firearms within the City limits". And that concealed weapon will almost certainly be prohibited because it has the capability to use a "large-capacity magazine".
A feuding neighbor who files a "domestic violence" or "child abuse" complaint may cause the discovery of prohibited firearms during a causal interview of the "Person-of-Interest".
Inevitably, a City staffer or elected official will be caught in violation of the ordinance, and subsequently excused from penalties on some very obscure technicality.
The Boulder ordinance is in gross violation of Colorado Preemption Laws (on matters of "Statewide concern"), not to mention the tattered Second Amendment of the US Constitution.
None of that really matters. The City Government is going to back this abomination to the bitter end. Boulder is a one-party State-within-a-State and the City Council members are quite secure in their jobs.
It will take legal action from outside the City to invalidate this ordinance, and large punitive damage awards to the inevitable victims of enforcement actions.
It will also take direct sanctions against the City in the form of cancelled Federal grant money and prosecution of City officials who violate Immigration laws in the name of "Sanctuary City" policies.
“They can pass laws, but whos going to enforce them?”
In CA these laws are nearly universally ignored.
I don’t know of anyone that has turned in a single rifle.
Of course, that makes range time hard.
It helps to dry fire and make mag changes in your living room.
That said, it’s nearly impossible to unlearn how to handle an AR well.
Why, the latest in Gun Control of course.