Red flag laws are a poison pill that likely won't see enforcement until additional laws get passed. It's an initial mechanism for door to door, though.
As I've explained in several threads on confiscation, any attempt at 'door to door' confiscation not involving anther countries' armed forces will not happen in the US, at least in our lifetimes.
There are several factors that ensure this, the first being with instant worldwide communication, it couldn't be done (or even planned) in secret. What, simply shut down the 'communications grid', you say? Works two ways, plus you'd have a bigger crisis to manage then, hundreds of millions would be hopping mad! The second, as I alluded to, is who are you going to get to do it? Local Law Enforcement? Yeah, there'll be a few that'd be all for it, until they start taking casualties, and they would.But most would not participate, or collude with owners (tip them off, etc.) Cops own guns too. Door to door confiscation in Germany in the 30's worked because so few (in the cities) owned guns to begin with, those who were not targeted turned theirs in voluntarily, as they believed themselves safe. (And for the most part were) The NSDAP controlled all forms of mass communication at the time, and had a pretty good, though not total, stranglehold on telephone and mail also.
So, now you think you'll get the National Guard to do it, or Active Army. Good luck with that. It won't happen with the current makeup of the Armed Forces, and the people who so desperately want the guns confiscated tend to be hopolophobic, so don't expect a mass enlistment of ANTIFA babies to go on "The Great Gun Confiscation Crusade".
Now we are down to allowing a third party to do it. There aren't enough mercs, er, contractors in the world to do it, and many of them (Thanks to GWOT) are Americans. So you invite China to come in and take all the civilian guns. Guess what? They decide to take the militaries', too, and oh, were staying, and thanks, American so called 'progressives', but you've outlived your usefulness, so up against the wall.