Not real certain what you are asking, but say you have a 30-06 - I presume that you want to have that barrel re-chambered to 30-06 again? And that barrel's rear end has enough "meat" left to do that - So, likely need to unscrew that barrel from receiver. Then, likely needs the barrel shortened at the rear, likely needs the barrel shoulder moved forward, perhaps a tenon thread added, then re-chambered. Is usually done on a "good" metal cutting lathe, not really a "specialized" lathe. Barrel tenon threads are cut with ground or purchased cutters at the appropriate angles - the new chamber will be cut with a "chambering reamer" and re-headspaced back to fit your receiver and bolt - I am assuming you are asking about a bolt action rifle - similar process for other action types. A lot to do with the person doing that machining, as to whether what you end up with is "better" than what you started with. Then, because the barrel has now been "set back", it will no longer fit into the stock like it did before - that might or might not be an issue. All gets a bit more touchy if barrel has iron sights on it or has scroll markings that you want back in same alignment. From my reading and understanding, is pretty much a "basic" gunsmith type job - of course, some end up with better results than others do.
