Nerf Grenade Launcher Attachement

Tools
1 drill
PVC Cement
Super-glue
Duct Tape

Materials
1 18" length of 1-1/2" PVC pipe
1 end-cap (also 1-1/2" PVC)
1 disc of plastic that will fit inside 1-1/2" PVC
1 spring (Recon CS-6 spring, or similar size)
1 1/4" diameter rod (Golf tee, or similar size)
2 strings
2 split rings (Like key-rings)
1 eye hook
1 Tactical rail mount (Recon sight, or the universal rail thingy from here: http://www.thingiverse.com/thing:16091)

1:  Drill hole in center of disc and center of end-cap.  Hole diameter should be just a little larger than the diameter of the string.  This is how you will cock the launcher.

2:  Place the spring and the pipe side-by-side.  Mark where the top of the spring is.  Drill two holes through the pipe.  Holes should be just a little larger than the rod, and about halfway between the end and the line you just drew.  This is the firing mechanism.

3:  Glue disk to one end of spring, and end-cap to other.  Thread string through holes.  Tie end of string sticking out of disk in an overhand knot.

4:  Glue pipe to firing mechanism.  You should be able to smoothly pull the disk back using the string.

5:  Tie one split ring to end of cocking string.

6:  Screw eye-hook into golf tee.  Tie string to eye-hook.  Tape other end of string to pipe.

7:  Glue rail mount to top of grenade launcher.

Firing
1:  Pull cocking string back
2:  Insert golf tee into apropriate hole
3:  Release cocking string
4:  Tilt part of the lid of a film-canister grenade off
5:  Drop grenade in, cup first
6:  Aim
7:  Pull the pin out quickly!