Lets start with the turret, since this is the fun part. Pop the turret out of the shell, it slides right out. On the back of the turret, there are 4 screws. Remove them, and your turret slides into three parts. This is the only one you need.
Cut the 4 screw ports that are sticking up at the top down, so that they are flush with the rest of the peice. Now, simply choose a barrel. I use CPVC, which fits very nicely into the 3 prongs in each space of the turret. Hot glue or Goop into place, and let sit until dry.
Now, lets straighten those barrels a bit. You can always print out the barrel spacer that Ryan made too keep your barrels inline. However, I dislike working with poly carb, so I used the end of a longshot dart chamber, which fit sunggly in between the barrels when lightly sanded. Pretty much any tube or even a Gatorade bottle cap can be used to center your barrels, as long as it fits straight. Then, hotglue into place. I then wrapped it in etape to make it look a bit more presentable, and for a slight stability increase. My barrels are now perfectly straight.
Now that your turret is steady and the barrels are straight, lets make it rear-load. For this, I unscrewed the white turret rotating piece in the back of the turret, and simply used a cone-sanding bit on my dremel to widen the wholes in the back of the turret till I hit the walls of the cpvc. Make sure to do this step VERY SLOWLY if you widen them with a dremel, for if they become to wide, they won't seal correctly. Go nice and slow, until they lie flush with the backs of your barrels.
Edited by ice, 17 August 2010 - 11:19 AM.