Killerk has posted pictures about his magnum but never posted the instructable so here it is.
Step 1: Create the Handle
1. Connect ten green connectors to a red rod and add the parts shown
2. Add 5 green connectors and attach a yellow connector to the top of the red rod
3. Connect two yellow connectors to the bottom of a red rod and push the rod up through the first ten green connectors, add the parts shown and push rod all the way up. Add a yellow connector to the top. Put a grey connector on a white rod and connect white rod to yellow connectors.
Step 2: Lower Barrel
1. Add brown connector to green rod on right of barrel at the top.
2. Slide white rod into hole of brown connector and connect two yellow connector's to the rod.
3. Swivel yellow connector's round to look like so and push two green rods in either side.
4. Connect a green rod to a brown connector and slide a white rod through the hole, connect two yellow connectors to it.
5. Attach to the rest of the gun with two green rods.
6. Snap the top off of a green connector and slide a white rod through it's hole. Attach like in image.
7. Create four more parts like in image 4, except the brown connector closest to swivelling brown connector should have no green rod on the right side. Attach two white rods between yellow and red connectors on each side.
Step 3: Upper Barrel
1. Create 7 of the same piece consisting of two yellow connector's, one brown connector, a white rod and a green rod. At the front of the gun attach a white rod to the brown connector.
2. Attach one of these to the white rod at the front of the gun.
Step 4: Connecting Upper and Lower Barrel
1. Make the part on the left once by connecting two yellow connector's with a green rod and connecting a white rod. Create the part on the right 5 times the same as the other part but without the white rod.
2. This is the firing pin, create it by connecting two red connector's with a green rod and attaching a yellow rod.
3. Slide the firing pin between the two halves of the barrel and at the back of the gun place the part that was on the left of image 1 over the two protruding white rods, place one of the other parts on the other side. Connect two parts together and attach so that one side of it is over two protruding white rods at the front and repeat for the other side.
4. Attach two blue rods at the back of the gun to the parts added in image 3. Attach one blue rod at the front as in the image.
5. Finish the front by adding two green rods and a brown connector
Step 5: Adding Rubber Bands
The Notes on the images show where they go.
Step 6: Firing
To cock the gun pull the firing pin back with the yellow rod attached to it.
The safety is the white rod sticking out at the back (highlighted in picture). To turn the safety on when the pin is bulled back push the white rod through ther hole at the top of the red conector on the firing pin.
To load put a bullet (image 2) in the orange connector at the front.
Just pull the trigger to fire.