I have been working on getting my igniter back up and going since my hiatus over the summer period. This has involved coming up a way to have removable but accurate orifices for the propellant injection. It took a while, but I found that a Lenox Laser 1/4-28 SS set screw is a perfect size to thread inside a 1/8 BSP nipple. I went for the optically measured option as this was the cheapest of which has a tolerance of 5% at 100+µm, more than good enough for this application.
My other bug to fix is that I was burning the electrode out of the spark plug, my injection holes are too close to it, so I will fix this by spacing the plug out a bit with more copper washers. Ultimately this will need to be addressed in version 2, of which I have a rough design nutted out and will start drawing up for printing later in the year.
(On a side note and abit of a plug, I am selling some SS tube which was intended for tanks, find them here.)