As far as defense against tyrannical government, guns are really a last ditch measure so it's really not accurate to categorize guns as the only means. The preferable measure is counter economics which forces the government to collapse or go full martial law. In the event of martial law. The US would lose all allies and would have war declared against it, I'd wager many US soldiers would go AWOL because they can't get payed and wouldn't kill their own, and the US couldn't arm itself anymore because their currency is valueless.