Machine guns to provide suppressing fire, semi-autos to take out the shooters.
Besides, if the Second Civil War ever starts, I doubt the military would be on the side of whatever fascist democrat was dumb enough to rip apart the Second Amendment.
Don't bet on that. When the confiscation order came down in the Katrina aftermath, NG troops where right there with the confiscation squads. If Martial Law is declared after another National disaster or terrorist attack, the troops will by and large do as they are told.