I originally designed and built this rubber-band crossbow gun back in 2008, before I had discovered Instructibles.com or seen any other k'nex gun ideas. I noticed one day that I had a sizeable collection of wheels, so naturally I just had to ask myself "What can I build to shoot them with?" Thus began several days of thinking, building, testing, and modifying; until I arrived at a solution that I deemed adequate for my needs. Since then, it has undergone several major revisions, such as the repeated tweaks to and eventual complete rebuild of the trigger mechanism. The belt clip is another recent addition, borrowed from a gun holster.

The PARTS LIST

-Rods-
grey: 6
purple: 2 (long & bendy)
red: 5
yellow: 2
blue: 9
white: 17
green: 16
TOTAL: 57

-Connectors-
white: 2
blue: 3
yellow: 7
green: 10
red: 7
light grey: 12
dark grey: 3
orange: 6
tan: 4
Y: 3
hinged: 2
-TOTAL: 59

-Other-
blue spacers: 58
Silver spacers: 16
1 grey gear
1 small tri-plate
1 small quad-plate
1 large rubber band
1 small rubber band

Step 1: Start Here

When built correctly, you should have symmetrical parts at the end of each step.

Hopefully, anyone will be able to build this from just the pictures, but if you have any questions, or something is unclear, please let me know and I'll try to clarify any issues.

Step 2: The Side-bars

Step 3: Trigger and Belt Clip

I designed the belt clip while making a K'nex holster for my Lego gun.
If you have a wrist-band, slip it over the tan connectors (while its on your arm) and then you can fire the weapon single-handedly by flexing your wrist downwards.

WARNING
The launcher could be loaded when you attach it to your belt . Without due caution, you may accidentaly shoot your foot (or the foot of a random person passing by).

Step 4: Its Just a Front

Step 5: Putting It Together

**Caution**
Do not expose the device to temperatures above 600°C as this may cause degradation of firing precision or, in semi-rare cases, complete loss of functionality.
Do not aim the device at humans (this includes your sister), animals, computer screens, windows, rare vases, etc.
Do not look into the operational end of the device, even partially.

Step 6: The Building Is Over Now

I, for one, congratulate my K'nex-gun-building Instructables fans!

Very good. You are now in possession of a K'nex wheel-launching device. With it, you can fire your own projectiles. These three-dimensional wheels have proven to be mostly safe. The device, however, has not...