This gun set is basically a hybrid of design elements from Red Impact and KillerK's gun. The only original, 'innovative' feature here is that they pull each other. Hopefully I won't get too much flame for putting KillerK's firing system to some creative use. :)
Pieces that will need to be modified/mutilated:
4x Dark Grey Connector (will be 'decapitated')
2x Tan Lock (will be weakened)
Step 1: Create Specialized Pieces.
Find a safe way to 'decapitate' 4 dark-grey connectors by cutting off the top halves of their loops. I stuck all of them on a rod and used a small hand saw. Makers of my Red Impact should already be familiar with these.
Also, we need to 'weaken' a pair of tan lock connectors so that they do not cause as much sliding friction on the firing pin they will be attached to. I have found an easy way of doing this that involves putting them on the end of a rod and turning them carefully. This permanently weakens the plastic and they'll never be tight again. I would mark them with a sharpie.
Step 2: The Firing Pin's Shaft and Trigger. (Rear)
Step 3: The Handle - Middle Section.
The camera flash was being kind of weird, and I was being kind of lazy.
Step 4: Ammunition Hopper - Front Section.
I'm still not used to my new macro close-up lens. The lens itself is physically in the way of the camera's flash light so when I'm too close, this happens. -_-
Step 5: Attach Segments Together and Add Structural Brace.
Step 6: Build an Identical, Symmetrical Mirror-image Copy.
Do they have to match by color? No.
Step 7: Assign Genders to Firing Pins and Arm Them.
As with nearly all firing pins of this type, it will violently explode if you don't use tape. Tape stops this by refusing to let the connectors widen up and detach. The best tapes are ones that do not stretch, like packaging tape or (I reccomend) alluminum tape. Wrap at least 3x around to be safe.
The firing pins must be powered by rubber bands. The anchor points for the rubber bands are are (opposite of the trigger side) the Structural Brace and (on trigger side) the blue rod of the handle. Take two rubber bands, bind them up, and stuff their combining knot into the firing pin's dark grey connector.
Step 8: Loading/Firing.
The intro video explains it best, but the way to very quickly pull back both firing pins at once is to hook the male into the female ends and pull on both. Be sure to hold them straight, facing perfectly away from each other. After the triggers auto-lock, separate them, aim, fire.