Second, I am always amazed how some gun owners undercut the RKBA.
1. It is useless to use firearms against tyranny.
Well, ignorance is bliss. Many might be unaware personally owned firearms were significant in supporting the Civil Rights movement against state sponsored or ignored night rider terrorists in that era.
Those who claim firearms are useless against a tyranny are the same ones who claim it would be nuts to try invading a country such as Iran based on the sole fact that it is 80 million people. But yet we're then told that a nation of 311 million people in possession of lots of arms would have any resistance crushed easily by a professional military force. If you have 1% of the population rise up, it would be 3 million people with arms. That's a hell of a lot to put down.
There are only so many places you can send tanks and troops and aircraft, and those require sustained logistics. Look up what Max Manus did to the Nazis in Europe during WWII. Blew up a supply ship, sabotaged rail lines, etc...tanks and aircraft don't move without fuel, infantry soldiers can't do anything without food and ammunition, etc...and unless you have a LOT of soldiers, maintaining a tyranny with an armed population is difficult.
If the government troops come with rifles primarily and the odd crew-served weapon or so and are rounding people up into trucks and so forth, it is hard to resist. But if the whole city or town is armed with rifles as well, then it gets a lot more difficult. You can't just knock on the door and say, "Get in the truck or else," because the person in the home can say, "Get lost, or else." So then you need to come in with the heavy-duty stuff, but that's then where you run up into the limits of numbers, logistics, etc...
2. A second undercutting of the 2nd Amendment is related. It is the folks who proclaim 5 is enough and those who have higher capacity guns are nuts or incompetent (if you can't do your job in one - blah, blah, tough guy). Or you shouldn't have an AR as you don't need them to hunt down Bambi or shoot Tweety Birds.
How you shoot when in an adrenaline-pumping situation is very different than how you shoot when relaxed, so such arguments about how much ammunition one "needs" is irrelevant. And then there's the whole fighting tyranny thing.