I have done it many times.
What I do is to cut off the shank if the action I am going to use has a thread well that is about the same size or larger then the barrel. I then turn a new shank and re-thread to the proper pitch and diameter, so it's not any different then starting with any contoured blank. You can also get rid of many chambers that way (not all, but many) and start over with your reamer.
If you are going from large to small (like using a 1917 Enfield barrel to go into a small ring Mauser) you simply turn the shank to the needed diameter and face it off to the correct length. Then thread.
The typical shank on most "take off barrels" is between 5/8" to 1" long, so you loose that much barrel length when you do this. Doesn't matter much with most cartridges but for the hot magnums it's not the best way to go. If someone wanted a 7MM Mag or a 264 Winchester you often benefit from length on those types of cartridges. But all the rest of the work is no different then ordering a blank from Shilen or Douglas. About the same labor, but the take-off can run from free to $40, and that sure helps the hunter who is in a tight spot and strapped for cash. I'll help a guy out when I can.
In every case I have done it I have come up with a totally serviceable rifle, and in about 1/2 the cases the guns shot extremely well, as good as starting with a new barrel.
