[rdl]

Might be interesting to print grip modules for firearms (Sig does the "TXG" series which are tungsten-infused polymer, used for adding mass within the defined shape/volume for competitive shooting/recoil reduction reasons. Due to the design of the firearm, the grip module is just an accessory and not a firearm and thus not regulated, at least under US law. Being able to print custom shapes would be cool. (https://www.sigsauer.com/p320-x-series-txg-grip-module-assem...)

[londons_explore]

The density is only 4 g/cm³.

You'd likely do better just machining it out of steel (5g/cm³, and much cheaper)

[rdl]

The 3D printers which can do metal (metal forge, etc) are incredibly expensive (100k+). I was thinking about custom to hand 3D printed grip modules, qty 1. Machining a grip module out of metal requires tools and skills beyond 3D printing, too. There are also some slight performance advantages of a polymer frame (grip module, in this case) over a metal frame.