Used a dremel with just the plain cutting disks to take out those sharp turns then the wire brush wheel attachement to smooth the edges. Then I added the criss-cross for a little better heat transfer across the die area, also with the cutting disk freehand. Not perfect but not bad. I left little nubbs instead of taking it all the way to the wall to give a little turbulence. Now it is just basically an open chamber which is all you need for the nb. And a lot less restrictive.