I have a 686-4 PowerPort that a Smith & Wesson-trained gunsmith declared as unfired because the interior of the port is unpolished, left in its raw porous surfacing, and is absolutely pristine. He stated that it is impossible to remove 100% of the combustion fouling three fired rounds would generate from such a surface, especially given how difficult it would be to get any kind of a tool into every area of the port. Those ports have a bottom, sides and an upper area that can only be seen with a borescope.
I am not a lover of porting of any kind and bought the gun just to have a nice example of something that I didn't think would be in production for a very long period of time (and I was right). I also agree with Muss Muggins about the turn line - all firearms have to be put through several dry-firing cycles to confirm functionality so a line has to be present on revolvers.
Ed
Maybe porting is done after the test fire?