What kind of gun exactly? I mean if you're going to go up against a M1 Abrams, a B2 Stealth bomber with "new-killer" payloads or an AH-64 Apache helicopter gunship, you're gonna have to have one mean gun. Even the Iraqi Insurgents don't have a fighting chance, and they have military grade explosives and RPGs!
The US Military is not allowed to act as a military against its own people. And, when the time comes, the people in those tanks and helicopters are Americans as well, they are not going to blindly follow orders and turn them against their friends and neighbors.
Guns are for sport and self defense. In the US we have the right to keep and bear arms. Many states allow open carry of firearms, and many states allow the average citizen to carry concealed firearms if they are properly licensed. I personally have a Concealed Handgun Permit and carry a firearm every single day.
Funny thing is crimes with firearms are not as "rampant" as non-americans seem to think. It is all about the media, which I would hope the average joe realizes blows everything out of proportion.