Could file a flat side on the firing pin and use the retaining pin to maintain orientation. Or you could print a small spacer to fill the channel, of the firing pin, leaving the flat side to Interact with the retaining pin. The spacer would be glued to the firing pin.
Need an SOT FFL (Special Occupational taxpayer) to build it. It's a machine gun. It would be an interesting challenge to make something similar with an frt. The trigger would somehow need to turn the crank.
I used a small flat file (from a needle file set) and hammered it through the channel to knock out the supports.
No, I still haven't got this one working right. I've been working on other projects lately. I'm thinking I might be able to get it running by modding the firing pin, or making a new one with a chisel profile.
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.
Could file a flat side on the firing pin and use the retaining pin to maintain orientation. Or you could print a small spacer to fill the channel, of the firing pin, leaving the flat side to Interact with the retaining pin. The spacer would be glued to the firing pin.