This is an Airsoft Grenade Launcher Kit.
It is a fully functional model, designed for 3d printing and it uses standard airsoft 40mm grenades.
It is very reliable because it has a simple push button as a trigger and a functional cross-bolt safety.
The launcher can be attached to RIS rails.
In addition to the 3d printed components, you'll need to source some other parts as follows (for reference, you can see the extra parts in one of the images) :
In the package you get all the files that you need to print for the launcher (+ 1 extra barrell model) in 3 file formats: STL, 3MF and OBJ.