I don’t know if there were .50cals set up in bunkers, but they were mounted on the appropriate vehicles. I remember a member of the church I joined after moving there was talking about that time. He was in the DC National Guard, and he spoke of riding around town in a duece and a half with his M-1 and the .50 cal mounted on it. He said that the ammo can in the feed tray was empty, the MG was merely for intimation, and he though it did a fairly good job.
The Michigan Army National Guard actually had .50 cals with live ammo mounted on some of their vehicles. At one point (in the book I noted) they thought they were under sniper fire and opened up on a couple of buildings in response. It was immediately after that incident that the 82nd Airborne was ordered in to replace the Michigan ARNG. Those MI ARNG folks who remained were stripped of all their live ammunition. The 82nd Airborne soldiers had one 8-round clip displayed on the shoulder strap of their web gear, and were told that if anyone loaded it into their weapon they would be court martialed. The lesson learned was that Regular Army soldiers were much more self controlled in the city and the “fear factor” of the locals, that these were
combat veterans, did the rest.
That was then, this is now. A very large percentage of the National Guard are combat veterans (The 34th Infantry "Red Bulls" replaced my company in Anbar, 2006). Both active and ARNG have hard-core, experienced soldiers, and both sides have knuckleheads as well.