Greatings, Gents. 3-19-07
This is my best Knex Gun of about 15 different homemade models. If you do not have a spring, you can't build a gun like mine. I have been perfecting this design for about two weeks. You will have to bild it from few pictures; My memory card only holds 7800 pixels (about 8 pictures, But there will be more than one batch of pictures)and dial-up internet is VERY slow. it has a few detachable parts, such as a Scope, Safty, and a Standy-Upy-Thingy.
While my pictures are uploading, I calculated some statistics:

Power level: HIGH
Provided By: at least 4 rubberbands and 1 Spring
Accuraccy rate: 95% with scope, 80% Without it
Range: 39 Feet with minimum Band & Spring (13 yards), 100 feet (about 33 yards) with my special Easy-Strech-But-Max-Velocity rubberbands.
Ammo Type: 6 Blue Rod Hopper or 12 Blue Rod Hopper (courtesy of Oodalumps with slight mod. {i think})
Cocking Difficulty: Easy

Step 1: Gather Parts

Rods:
Green 2
White 2
Blue 2=6 for ammo
Yellow 6
Orange (flexable) 2
Red 4
Grey 3
Black/Semi Transparent 1

Connectors:
Grey 1 clip 14
Orange 2 clips 10
Red 3 clips 9
Green 4 clips 11
Yellow 5 clips 13
White 8 clips 10

K'nex Misc.:
Blue clips 3
Grey or Tan Clips 12
Blue spacers 16
Grey spacers 2

Other:
2 normal rubberbands
1 long rubberband
1 small rubberband
Glue (optional)
Tape
1 Spring (like from a bobble head or a hardware store.)

Step 2: The Barrel (end)

This is were the firing pin and trigger are. Build everything above my hand. Put the trigger on the right side.
if for some reason you cannot tell what the parts are, they are in this order: 5 Whites or Blacks, 1 yellow, trigger, 1 yellow, 4 whites or blacks, a space but not quite a blue spacer sized space, 1 more white or Black.

the firing pin is shown in this picture. it is a grey/balck/kinda clear rod with a spring attatced to it through a orange connector. BUILD THIS BUT DO NOT PUT IT IN YET. Modify it by putting tape on it to help it absorb the shock.

Step 3: Hopper and the Front of the Barrel.

This is Oodalump's hopper. I give him 14 % of this instructable's credit The top will only go on one way.

To make it a 12 rd., remove the grey block and insert it in a down position. Then remove two clips from both top sides, and put an orange straight clip there. Do the same thing you did to make the lower extension. NOTE: YOU CAN'T USE THE SCOPE WITH THIS HOPPER. IT IS TO HIGH.

Step 4: Build the Handels

self explanatory.

Step 5: Special Features...

1. Scope
2. Saftey
3. Stand

Ha-Ha!

Step 6: Puting It Together

1. Hold your barrel.
2. Take the green handel and slie its' protruding yellow rods in to the first 3 white clips while retaining that small space at the end of the barrel.
3. Clip the saftey onto the oter end of the barel with it's diagonal orange clips facing the outside.
4. put the yellow handel on the front by 1, cliping the red 3 clip on to the lower blue rod & 2, puting the flexis on the opposing side. I tape my red clip so that it won't come off. (if made correctly it will pop of; it doesn't clip on well)
5. Put the scope's white pegs into the red front clip and the first white 8 clip. You will need to remove the scope each time you reload. The fastest way is to break off the rear white rod and swing the scope out without fully removing it.

Step 7: Springs and Bands/Loading and Firing

that little space in the rear is a spring anchor. Bend the spring tip a little so that it will fit through a clip and out(rest in) a Quadrilateral hole. put the other spring end through the hole in the clip.
Now the rubberbands: put a small band in that little crevice that you made for the spring and in the end of the orange clip. Put a Large rubberband in the clip an at the bottem of the hopper(under the barrel). The final band goes at the top of the trigger and at the end of the green handel.

Load by puting 6-7 blue rods in the hopper.(self-explanatory)
Pull the firing pin back so that the trigger snaps into place. flip the trigger. repeat 5-6 times. Reload. Repeat......