This is my 45° angled version of the launcher. It also has a bit smaller tolerances if you use the original plunger from the source object by LoboCNC: https://www.thingiverse.com/thing:5214201
(EDIT: THIS WAS DELETED BY THINGIVERSE; IT WAS NOT THE AUTHOR!)
Here is a substitute from the original designer:
https://www.prusaprinters.org/prints/131862-desktop-whomp-rocket/comments

I know there are several angled versions but I didn't find them very appealing, so I made my own.

This has a lot of ooomph if triggered with a fist slap, so please be careful not to aim at a person or an animal. Use with care!

You find the plunger and the rocket stl-files at the source object.
(THANKS THINGIVERSE FOR DELETING IT :-(((( WHY??????
Have fun!