I have been printing with the V6 for well over 4 months without any problems. Recently my filament kept getting jammed. In the beginning all I need to do is remove the gunk to clear the jam but recently it is happening too often. I looked inside the brass nozzle and to my surprise I could see concentric rings (that look like shallow screw thread) inside the nozzle. I compared that with a spare 0.4mm nozzle. While the inside of the spare nozzle is not exactly smooth, there were no spirals. Is this due to wear? I am surprise polymer filament could wear out the nozzle in this manner? OK so I have been toying with several exotic filaments such as Brassfilled, Bronzefilled and Carbon Fibre from Colorfabb. Is this kind of wear expected? I mean causing what looks like concentric rings or spirals in the nozzle. Is it OK if I use a drill or reamer to 'remove' the concentric rings/spiral in the nozzle? Anybody else has the same observation?