When I toured the Krieghoff factory a few years back in Ulm, Germany, they showed me the tool they used to straighten barrels. It was not much different than what Stan described. If I remember correctly one of the posts you would rest the barrel on was actually a concave wheel that could be moved along the length of the barrel to the right spot. The gunsmith would just apply pressure once the two points of contact were where he wanted them.
The part I remember more distinctly was that the guide illustrated it had to be in an area were the gunsmith had the right kind of light to be able to see the bend and be able to adjust it correctly.
