Sirkis also explains the reasoning behind the interference-fit barrel, as opposed to a threaded barrel. Threading also introduces some problems. Obviously there are two sets of threads to cut and they have to be just right so that when the barrel is torqued-in, the extractor, cut will be in the right place. In a way, threads provide two opportunities for something to go wrong. Kimber's manufacturing is well suited to turning round parts, or reaming round holes to very precise sizes.
Steel expands when heated.
So a very precise fixture was made to hold both the receiver and the barrel in proper alignment. Propane torch heads are mounted on either side of the receiver. When everything is lined up, an insulating material is placed between the receiver and barrel and the torches lit. Even so, it takes quite a bit of leverage to seat the barrel. Variations of this method are used in the manufacture of many rimfire rifles.