This time, a combination of the knurling library, Fusion 360's threads, and a silencer design from Thingiverse. After much wrangling, I fixed a few issues with the original model and printed this off in around 8 hours, slightly slower than usual, at 100% infill Black eSun PLA. Really looks the part and completely stunned the lad who ordered it. It wasn't all sunny though. Initial test at 18 ft/ lbs no problem. Stepped up to 50 ft lbs and fairly surprised it survived. Final test at 75 ft lbs killed it. 8 hours to print, 10 mins to kill. Have done some thinking and a bit of maths and hopefully a redesign should be able to handle the extra pressure by enlarging the initial chamber using a cylindrical (instead of conical) design.