This is the Super Maul, with VERY much firepower, can shoot a pencil through a Coke bottle.
Not very hard to make and you can buy all parts in shop (or order) Ideas and pictures from http://www.officeguns.com

Guys I just want to apologise for copying everything from officeguns. I HAVE made one myself but I just haven't taken any pictures of it because I thought "They are all on the Internet, why should I take myself?" Sorry for that.

Step 1: Parts

all you need is: (you can order the Maulys, but you can also go to a shop.
1. broad rubber band.
2. 3 Mauly 32 (order them here: http://maul.de/php/Proxy.php?purl=/maul/products/catalogs/1000116/10/7/show,49.html
3. 4 Mauly 51 (larger than mauly 32) (order them here: http://maul.de/php/Proxy.php?purl=/maul/products/catalogs/1000116/10/7/show,51.html
4. Things to shoot with.

Step 2: Assembly

1. Remove the handles on the Mauly 32's. Mount a Mauly 51 on the outside of two Mauly 32's as seen in the picture.

2. Mount another Mauly 51 on the end of the Mauly 32 which isn't entirely covered by the first Mauly 51. Then put the third Mauly 32 on the end, as seen in the picture.

3. Remove the handles on the two Mauly 51's. Then flip the gun.

Step 3: Assembly 2

1. Put the rubber band around the row of Mauly 32's and mount a Mauly 51 on the outside. Make sure the rubber band isn't caught between the Mauly 51 and the rest of the gun. It has to be able to travel freely.

2. Mount the last Mauly 51 the same way as in the last step. Remove the handles on the two Mauly 51's. Make sure the position of the two Mauly 51's on top is offseted a bit. This makes the gun more stable and easier to fire.

Step 4: Final Step & Firing

1. Stretch the rubber band and put it along the outside of the gun. As seen in the picture, there should be a double layer of rubber band on the end of the gun. This makes the gun fire with more power.

Now insert a pen in the Mauly 32 and pull the rubber band. Release and it fires! WARNING! THIS THING IS VERY DANGEROUS!

You can also attach a laser pointer at top of the gun for better aiming.