Magazine design: www.instructables.com/id/Easy-Lego-Magazine
Step 1: What You Will Need:
1x 10x4 piece.
3x 2x4 piece.
1x 8x1 flat smooth piece.
1x 1x4 flat smooth piece.
2x 1x2 flat smooth piece.
1x 1x20 (make up from smaller pieces)
1x 1x22 flat (to go on top of the above)
1x 1x2 with pin sticking out of the side.
1x 2x20 (make up from smaller pieces)
1x 2x22 flat (to go on top of the above)
1x 2x2 with pin sticking out of the side.
1x 4x22 (just make it out of 4x2 bricks and you're fine)
See the picture below, on the left is the base, middle is the walls and right is the top.
Note: the flat bricks aren't in the picture because I'm lazy.
Step 2: Construct The Base.
Take all the parts from the BASE parts list and arrange them like in the first picture.
When the gun gets built there will be a gap in between the 6x4 and the 10x4 of 6 spaces for the mag.
Step 3: Make The Walls.
You need to take the parts from the WALL list and make a 1x22 piece including the piece with the pin and place a 1x22 flat line on top to form one wall.
The next wall is formed by a 2x22 piece with a 2x22 flat piece on top, try to get the piece with the pin in the same place as the other wall, it doesn't matter if it is off though.
Step 4: Put The Walls Onto The Base.
When you do this, make sure you have the pins facing outward and that you have a 6x1 gap in the base for the magazine.