This is a double shot modification of my K'nex gun.

The original is here: https://www.instructables.com/id/Knex_gun_29/

Step 1: Gather the Parts

(The parts are said in the standard colors. The pictures may differ slightly.)

2 single shot K'nex guns Here.
2 bullets
2 white rods
2 grey connectors

Step 2: Assemble

1. Attach a white rod to the bottom of the green connectors
2. Attach a white rod to the bottom of the yellow connectors
3. Attach a grey connector to the white rod connected to the green connectors. This needs to face up, so it is obscured by the green connectors.
4. Attach a grey connector to the white rod in the front of the gun, facing forward (as opposed to up).

Step 3: Fire It

1. Pull back the orange connector(s) as far as possible
2. Place a bullet(s) in front of the orange connector(s), in between the two sides of the rubber band(s)
3. Slide your finger out of the way quickly