The process is fairly simple. The action wrench(there are several varieties) clamps to the action in such a manner that it won't slip or mar the finish. The barrel vise is usually a couple pieces of steel with 2 blcoks of wood clamped between. The wood blocks are bored at their junction with a hole the diameter of the barrel. The barrel is clamped in the vise, as close to the action as possible, and rigidly attached to the bench or some solid object. The action wrench is attached to the action and it is simply unscrewed from the barrel. The tools used are built in several configurations and of course a witness mark should be applied to the barrel and action so that they can be returned to the exact same positions. The Remington action uses a washer, sandwiched between the action and the barrel and extending downward, to act as a recoil lug. This has to be retained in a verticle orientation as the barrel is tightened. Some of the action wrenches handle this and some relie on a seperate holding device. Done properly and assuming there are no unusual problems the process can be accomplished without damaging the finish..
As to the proting, they may not have removed the barrel. A lot or porting is done using a process called EDM. Basically an electric arc is used to vaporize the metal and a fluid is forced between the material and the electode washing away the removed material. This is a very precise process and the action may simply have been left in place..
