As of 5/27/15 I have been notified that there is a design flaw that makes the unit non functional, thanks to meendiz for bringing it to my attention details below.

It has been brought to my attention that the barrel diameter is improperly sized to accept 40mm grenade shells as i have mistakenly sized the external diameter as 40mm rather than making the internal diameter 40mm, i will try to have the updated files poseted by the middle of June or sooner, i apologize to anyone who may have spent time and materials printing the defective unit, please bear with me this is a prototype and my first heavily detailed design, thank you for your patience.

This is a prototype for a 40mm grenade launcher for use with 40mm Airsoft gas grenades, this is my first attempt at making something like this so it may need a fair amount of sanding and fine tuning before it actually functions, some assembly required, always use eye protection when shooting airsoft replicas, thank you!
Major update time! (3/31/15)
So, I started on this prototype on 3/30/15 and now its time to post a revised version! I spent about 3 hours cleaning up the edges, adding a few new things, changing some others and overall making a better launcher (I hope)
Changelog
added slots in top of grip/receiver for the latch rails
added front and rear "iron" sights
added some makers markings on the backside of the grip/receiver
fixed the problem of a free-floating firing pin (I hope)
cleaned up the edges on the trigger and grip for better ergonomics (the grip will require some sanding)
re sized latch
fixed the possibility of latch coming off if pulled too far
added cutout on side of barrel for easier reloading
*shortened firing pin for better fit

That's all for the changelog so far I will remove the old files and add the new ones along with a better set of instructions and an exploded model for you all to look at.