People are printing guns. They're printing guns right here in the UK.
Then they're taking them out to the firing range, setting them up on a test stand, firing them by remote control, and filming the ensuing carnage with high frame rate cameras.
If you make a really really good 3D printed gun, it'll last at least two shots before it explodes into about a trillion razor-sharp fragments expanding rapidly outwards from where your hand used to be. The way you tell it's a really really good one is it didn't explode into a trillion fragments on the first shot.
We've seen enough Terrifying Public Information Films about the dangers of fireworks to mess with that shit.