During the American Revolutionary War/Napoleonic War, do you know what a local militia with muskets or even breach loading rifles were good for? Sending into the meat grinder and taking out with artillery.
The ONLY time The Holy Second Amendment was ever a threat to a government was, funny enough, "The Wild West" in the US. That brief window where logistics made deploying the military difficult but everyone and their mother had repeating rifles and pistols and could even get a gatling gun for not TOO much money. Which, funny enough, led to the rise in what were basically PMCs to take out said ruffians and has persisted to today in the form of the over-militarized police force and the idea that you need a full kill team in every village.
As for "Just fight a guerilla war": I am not interested in the American Revolutionary War (even though all the same arguments hold true...). The US and Russia have both bled and eventually abandoned countries like Afghanistan as the losses became too high to justify the occupation. But basically any time there was a stand up fight, they won overwhelmingly because of things like Helicopters, Tanks, and Artillery.
But then you look at groups like ISIS and warlords in Africa and the chaos that was left in the wake of South America. THOSE forces defeated their guerillas. Why? Because the occupying force actually gave a shit about the land and wanted to keep it. And they didn't care about public opinion on what they were doing (see also: Israel's genocide). Some kids run out of the woods, shoot a few people, scream "WILDCATS", and start macking? Cool. Go round up a dozen people in the town square and execute them. And make it clear that if said wildcats aren't turned over by next week, another dozen people will be executed. See how fast support for the guerillas goes away. Even better, you know they are hiding in the suburbs near Delancy Street? Set up a perimeter and go door to door executing people until you find them.
Which gets back to your super timely example from the 1700s. Where the Brits basically said "Fuck it, we don't care" due to the colonies being a whole ocean away and increasing unrest in India. And... India was a LOT more valuable than a bunch of jackasses who didn't want to pay taxes.
But hey. I am sure with your rifles you can totally lead a guerilla war that makes the republican government abandon the United States because casualties are too high, I guess? It worked for Captain Soap in Call of Duty maybe?