Tank bulkheads:
After machining the original bulkheads we saw the improvement of the one piece bulkhead as done on the excellent Sinnoh Sphinx+ build. We quickly realized the dual o-ring design was more in line with our previous rocket motor builds and were happy to adopt the upgrade in the NITROCAT as we didn’t machine the retaining rings yet (which we would have modified by using a 100x10mm tube with integrated threads so it would not use the 3d printed nut retaining ring). Machining the internal bore of 90mm deep proved quite the challenge with the stringy aluminium not clearing the bore. We got it done by frequently stopping the machine and manually removing the bird nest. We are not giving up and ordered a PCD insert with chipbreaker which hopefully help us breaking a chip at moderate feeds and speeds. Through tool coolant would have helped a lot but not available on our machine. We changed to 12x M6mm bolts for retaining the bulkheads in the thin walled 100x3mm casing, more on this later. Dual o-rings 86x4mm NBR 70 were used to seal the tank. We are very please with the fit and it seems to be a big improvement on both the oxidizer as well as the fuel side of the tank. Does any catch the crash (e-stop to the rescue) in the toolpath picture?

Piston:
No significant changes but modified to accept the same metric o-rings 86x4mm NBR 70 as the bulkheads.