"Civilians arming themselves against the tyranny of the state has been an outdated idea since about WWI."
- Said Muammar to Hosni, as they sipped tea with Bashar
In Lebanon, Western air strikes leveled the playing field; they took out most or Mummar's forces.
In Egypt, they didn't have to fight the army; the army abandoned the Hosini.
In Syria, the army split, and they're mired in civil war; Bashar remains, tenuously, in power.
What about Bahrain? There the army (and the more powerful armies of the neighbouring Saudis) has stayed unanimously behind the throne, and the revolution was pretty much drowned in its own blood.
The premise that civilians cannot fight the state
by themselves seems hold in these examples. It looks to me like you need military intervention, from outside or inside of the state to have any hope of making a dent. And note that none of these Arab regimes were anything nearly as well armed and organized as the US military.
Now, the US military is very unlikely to want to go in for the wholesale slaughter of civilians on US soil. Again, though, tyranny doesn't happen in a vacuum. Italy, Germany, Hungary all
elected their fascist regimes. If it happens in America, it will because your neighbors want it to. In which case it's not a wholesale slaughter of American civilians but a few "terrorists"/"patriots" being quietly (or not so quietly) disappeared. I do not see how your guns help you, then.
I can't see how it would be FBI/DEA/BATF against "the rest of you" -- the FBI is also made up of Americans same as the Marines. If it comes to armed revolt, why are they more likely to stand with the regime than the oath-sworn military officers? Maybe they are, but I don't see it. Our military would certainly side against its people; they have a very "them and us" mentality which I suspect the powers that be deliberately cultivate. Perhaps America is different. Regardless, don't police forces in your country now also find themselves armed and armoured on the federal dollar? I keep hearing in the news that Sheriff's offices can pick up
In any case, you're talking about being part of a widescale revolution, however. For that to occur, the United States would have to (with the tacit approval of its populace) fall into tyrrany, and THEN the tyrants would have to bungle the job and lose that approval to the point of triggering a general revolt. That is a process that can take decades. (In my reading of history, the masses are usually less concerned about freedom than having full stomachs. The French, Russian, and Arab Spring revolutions were fundamentally bread riots at heart.)
Probably, in the meantime, they're going to outlaw your guns, sift cyberspace, and come a knockin'.