When government tyranny gets to the point of trying to blatantly confiscate firearms, I don't think that the only weapons at the freedom fighters' disposal will be the guns they have in their homes (i.e. shotguns, handguns, rifles)?
At that point many National Guardsmen and active duty military may make the decision to side with The People. There are plenty of liberty minded folks in the military that would get a wake up call. If/when they make the decision to side with the people, then some state NG armories and even US gov't armories will begin supplying the revolutionaries.
You may see "rebels" fighting with just with civilian AR-15's/AK-47's and IEDs at first, but it will evolve to them using tanks, artillery, helicopters, machine guns, missiles, grenades, etc. You'll see not only retired, but "active duty" NCOs and even Officers fighting alongside and leading them.
In Iraq, Afghanistan, Libya, etc. the people have acquired use of mortars, rockets, artillery, etc. in addition to the IEDs we hear so much about. And we have far more of those types of weapons scattered all about the US than they did in Iraq or Afghanistan.
I could be wrong, but I doubt it would be just "farmers" vs. the Federal military/law enforcement agencies like some say. I think it would be far more complicated... and bloody... than that.
Our family's journey from the Rocket City to the Redoubt: www.suburbiatosimplicity.com