Tabletop model of a grenade for 3d printing, which also serves as a container. It's not entirely accurate (the design model was MK2), but it still looks pretty convincing. If you use a spring or rubber band, the safety flies off when you release it. The thread has a small offset, so the lock is pretty tight.

I think, that it's a little bigger than a real one, but you can scale it in a slicer software, if you want to.

I also tried to scale it to 50% of the designed size to print it as a keychain. Unfortunatelly, it's pretty hard to close. The small size needs few adjustments, especially in the main thread design. Might come in the future.

Except the printed parts you will need keychain ring, pliers, wire ∅ 1.0 - 1.5mm (binding wire works fine) and a spring (cca 5 x 20 mm) or smaller rubber band. 

As you may have noticed, the only component that needs suppports is Safety. I recommend making supports only on the edges to make it easier to remove them later.

To achieve a nice result, consider printing the first few layers (approx. first 4 mm) of the BodyTop component in yellow.

To install EjectorLever component, you can use a wire. Create a hook and pull the spring or rubber band on the bottom of Top component as you can see on the image.

Then click the EjectorLever on the axis in the middle of the BodyTop component using pliers or some narrow tool.

The pin is made from the wire. I used a binding wire, which is often used for gardening. Use pliers to make a loop at the end of the wire.

The rest of the assembly should be pretty straightforward process.