So, from my experience with the NaG (I've built 3, 2 have exploded)...
Issues with loading/firing/extracting are usually down to the chamber geometry. You need to sand or file a slight cone into the chamber (for extraction) and a "feed ramp" into the top and bottom of the breech end of the chamber (for feeding).
I used rifled barrel liner for all my builds. The scuttlebutt is that a smooth 6mm ID 8mm OD stainless pipe will work better, because it produces less back pressure.
The best way to taper the chamber seems to be chucking the barrel into a drill and wrapping a piece of sand paper over a small rod, held at an angle, while the barrel spins.
I have a video on my odd sea firing the NaG https://odysee.com/@FieldExpedient:6/NaG01:e





I'm planning a version for the Decker 9. Currently working on the Thompson .45/9 beta at AWCY?
I'm a little too excited.