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.
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
Remove the handles on the two Mauly 51's. Note that the gun has been flipped around in the picture.
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.
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.
This is the final step. 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.