This will be a hot take but I think the community is too conservative with materials. I understand that printed bang sticks are inherently dangerous and it's best to be on the safe side, but there was a guy on reddit who printed launchers out of ASA only and got shit for that despite having working proofs. There even was a guy who posted a beautiful Urutau made from Creality Hyper PLA-CF and claimed over 100 rounds without signs of damage. OG FG…

How DIY do you wanna go? Easiest is typically Glocks and M-11/9 builds because the territory's well-tread, most comprehensive total-DIY project is easily the FGC-9 MkII, but you'll be tooling up for ECM, which is a fairly tall upfront cost of time and discipline.

Have a look at this release -- it's a tutorial on doing up a feed cone. I'm not sure if there are instructions in it for adapting this to an FGC-9, but if there are, this'd be your best bet:

https://guncadindex.com/detail/Barrel_Feed_Cone_Tutorial:a