What is your idea of an ideal gunsmithing lathe?
Mine would be a Talisawa 13-40. 1 1/2 spindle bore, short headstock for chuck and cathead barreling, and a bed long enough for taper turning barrels.
A Weiler Condor would be even better, or a 10L longbed Southbend as a good but not great choice.
If your barreling 50 BMG or making a 50 reciever, something bigger than these would be ideal, in my expierience.