This was interesting...9X25 Magnum Bullberry T/C barrel, 10mm Magnum necked down to 9mm.
Very interesting to see this was done...
The article referes to using 357 dies (SIG) and the angle of the cartridge neck shows it but you can clearly see the spent case shows the change because the chamber is cut from the 9x25 Dillon reamer not the 357 Sig like the shoulder on the loaded rounds...
See the Gun Broker listing...
http://www.gunbroker.com/Auction/Vie...Item=225458739