It is always interesting and encouraging to see such legislation proceeding in the states. Others, such as Wyoming, have actually passed such laws including criminal penalties against any federal officer attempting to enforce new and restrictive firearms laws within its borders.
Realistically such state laws are probably symbolic at best, really little more than sending a message to Washington, DC in hopes of telling federal authorities to back off on this issue. I would expect the fullest possible demonstration of federal power against any state that attempted to enforce such laws. It wouldn't surprise me if USDOJ has already drafted the writs of habeus corpus to spring federal officers, and arrest warrants for state officials involved, ready to fill in the names and dates and take to a friendly federal judge for signature.
It would provide a very entertaining dust-up if such confrontations ever came to pass. Is a state governor ready to call out the National Guard to back up state and local authorities in a confrontation with federal officers? Are state National Guard officers (and troops) willing to stake their commissions and futures in order to comply with state orders, probably in light of simultaneous 'federalization' orders from DC? Might it happen that any such actions be interpreted as being in an open state of rebellion, justifying the imposition of martial law (suspension of all civil liberties during military occupation and control)?
Even if none of the above extremes came to pass, we can be pretty certain that every single dime of federal monies (highway funds, education funds, food stamp funds, unemployment funds, and all the other purse-strings controlled by the federal government) will come to a complete halt immediately. Restrictions on banking and commerce would also be very likely.
In short, when push comes to shove a state government would have to realize that it is within spitting distance of a civil war.
