LXV Airsoft got an assembly guide for those who purchased their 3D-Print Design for the RPG-26 Airsoft Launcher... "This Airsoft RPG-26 uses 40mm grenades including Taginn Shells. You will need to make yourself a sleeve for the shell as the barrel is a little wider. And different 40mm grenade types make it impossible for me to provide the adapter for all the grenades.

It has been tested extensively and works well."