This is my very basic K'nex ACOG scope, inspired by Modern Warfare. It's mainly built from broken red connectors but is pretty good at it's job
Pros:
Good looks
Simple
Adjustable M16-style reticule
Good visibility

Cons
Not a real ACOG (yet)
needs many broken parts, which can snap when built

Check out my new ACOG v2, inspired by Trijicon's TA01NSN-RMR series!

Step 1: Parts List

this is what you need:
8x red connectors
6x yellow/graphite rods
6x dark grey connectors
6x tan clips
1x ball joint (may be wrong, so just look at the pictures)
1x black hinge
2x blue spacers
and anything you want to add to it

Step 2: Body

make the ACOG's body
1) first, you'll need to attach the broken red connectors to the rods as shown
2) repeat at the other end

the broken red connectors are designed to increase visibility down the scope. This allows a greater chance of seeing your target in combat

Step 3: Sight

This is a simple step.

1) attach the ball joint piece at one end of the scope
2) attach the hinge joint at the other, behind the red connectors as shown

These additions allow you to aim properly at your target

Step 4: Rails

This step allows you to attach the scope to other K'nex guns.

1) attach the tan clips
2) attach the grey connectors and link to the tan clips (as shown)
3) slide the graphite rod in
4) secure the graphite rods in place.

The rails allow you to attach the scope to any K'nex gun with little modding