KISS works or 15 yo "invents" 3D printed slug
 

https://www.youtube.com/watch?v=AlIDQCgZoUc

It's an enlarged .177 pellet design, but it works, you can DIY at home, and no one else seemed to have the initiative. Good for him!

The rest is up to imagination i.e. Another video shows carbide-tipped that penetrates AR500 steel.

How long before your 3D printer requires same headache as NFA items :D