If this hypothetical tyrant/dictator has the support of the military, there is not much of anything regular citizens would be able to do about it. It seems to me that with what the modern military has at its disposal any insurrection would be put down swiftly and with catastrophic loss of life. I'm sure you could come up with an alternative scenario where a small group of citizens with their ARs are able to resist, but it's not credible. People have lots of reasons to own guns: they hunt with them, they want one for home defense, they are into target shooting, they are planning to kill people with them, holding a gun makes them feel strong and they wish they could fuck their gun. All of these are more plausible than owning a gun to resist the state.