A common scenario I hear voiced on gun fora and elsewhere on the intertubes is that sweeping federal gun bans of the "turn them all in" variety are unlikely, as is some sort of coordinated door-to-door "sweep and clear" gun confiscation, and so how the government is going to take away all the guns is this:
They're going to take away the guns of gun owners a few at a time. A Ruby Ridge here, a "barricaded whacko" there... And pretty soon there'll be nobody left to stick up for you when they come for your guns!
Thing is, they'd need to close off new gun sales at the same time, or they'd never be able to Randy Weaver enough people a day to make up for that day's first-time gun buyers. And closing off all new gun purchases would kinda telegraph the punch, I think.
But suppose they did close off all new gun purchases, and then set about manufacturing a hundred Ruby Ridges and "barricaded whackos" a day. How long would it take?
Well, let's assume the "80 million gun owners" number is reasonably accurate. Given that assumption, even if they did cease all new purchases and
confiscated the guns of 100 gun owners a day, the last guy would have
2,192 years to wait before they finally got to him, so it's not like he
wouldn't have plenty of warning.
It's something that a lot of people on both sides don't really process: The scale of the gun culture in America. If they want all the guns, they're going to need to get them in some way other than onesie-twosies.