Having read all nine pages of discussion about nerf nades, mines, tripwires etc on NHQ, I came up with my own idea. It is to be a UGL launched grenade, that can be filled with anything - foam, BBs, even paint.
Original topic if you're interested. I suggest you read it; it provides a lot of background information about the development behind it and problems it's overcome etc.
My original idea was for a cork based design (see topic for details), however with Davisev5225's help, we've developed it into much more...

Currently:

What I propose to do. Note that I'll remove the little lip inside the capsule. The catch is pretty self explanitary - credit goes to a nerfing friend when he was looking at the bolt sled for the Recon. I haven't drawn in the rest of the chamber since thats piss easy compared to the catch and hasnt got anything to do with the mechanism.

I'll add a rim to the detonator so that when it impacts, it pushes the catch inwards (from holes in the capsule).

This forces the baseplate backwards with lots of force. It will stop at the end when the catches engage two more holes at the bottom. Note that the spring also pushes the detonator forwards again.

My main aims for this are as follows:
- To make a successful, working Nerf Nade.
- Made cheaply out of readily available materials - so they can be mass produced by anyone
- Once the grenade is finished, I intend to make an underslung/underbarrel grenade launcher, either out of the LS front gun, or from scratch.
Please discuss - comments, questions, suggestions all welcome.