Don't.
That's a really crappy and more than a purple dangerous design. There's way better stuff you can build if you want to print gun stuff.
Discussion
What should I be looking at instead? Isn't the FGC9 battle-proven?
Anything designed since then? It was a bad design stolen (via lack of proper attribution) from:
https://www.youtube.com/channel/UCELUIVhFl7I-gibXb5vUGLQ
Derwood is one of the best in this space.