The tapered fitting your gunsmith is talking about is the same system that is employed by the Cam-Lock system used to mount lathe chucks onto the lathe spindle. It works very well but requires super precise fitting. The threads often used are either ACME (29 degrees included angle) or Trapezoidal (30 degrees included angle). These types of threads have greater root thickness and the steeper thread angle provides less splaying of the thread under load. They are often chosen where a segmented thread is used. The German gunmaker Theo Jung uses this system.

http://www.waffenjung.de/?take-down,60

Waidmannsheil.