Louisiana is very strange. Their law, founded on Napoleonic code, holds property over people.
It's pretty much unique in the U.S. The law is pretty much if anyone, including police trespass without notice, you may shoot them. Bing!!! Light goes on.!!! No wonder the police were so worried about guns down there. Entering on a persons property, with that law in place, made them VERY nervous, and scared. Now it starts to make a bit of sense. Not good sense, just sense. Rather disarm all citizens, then take the chance one of them legally justified, shoots an officer, by accident or not. So, they get out the records of who has registered their guns, and, confiscate them, making sure THEY are protected, but, throwing the citizens to the dogs, or criminals, if you would.
Given that is the law, and, most law folk are indoctrinated in liberal ideology by their law schools, it's not a great shock that something like that should happen.
Now, the disaster I spoke of was Jan 1, 1982, in Capitola Kalifornia. Power was out for 3 days, torrential rain, and flooding, after long prior periods of rain. No place for the water to go, so, power out, sewers overflowed, creeks turned into raging rivers. Mudslides, giant redwoods going 35 miles an hour, down the middle of a river that used to be Soquel Creek, and knocking bridges out. It's on record, and, I've posted that experience more then once, not going to do it again. The police officer came down the hill because he heard a gun shot, and, was investigating where the shot came from. Was he checking on us to see if we were all right? Perhaps, perhaps not.
What I will say is one look at the Rott removed any sort of chippy attitude from his voice, and, in talking to him, it was REALLY noticeable, in his attitude, when he noticed the dog.
You seem to focus on the M16 part. When someone has an AR-15 with a selector switch, it's not distingushable from a normal AR-15. Needless to say, no one volunteered to demonstrate the guns in full auto, even though that was before the ban, the modification, putting in the selector switch, was still illegal. Also, covering positions are best being just that, without the person at the door being aware that they, and you are covered.
Now, you ask how people having weapons could have stopped the gun grab. Again, I go back to the Rodney King riots where the police pulled out, along with fire departments, due to being walking targets, and, let the people fend for themselves. The police also did not charge the barricades in the Pacific Palisaides with guns blazing because legally owned guns were protecting their own property, and neighborhood.