Step 2: Make the Ammo Barrel
Cut a piece of sheet metal into an 15.5x30.75" rectangle. I recommend sheet metal from the air duct section of Lowes, it's much cheaper than the actual sheet metal sold with the steel bars and such.
Mark a line down the short side 1/2" from the edge. Every 1" to 1.25" or so put a mark for a rivet. We made ours unevenly spaced on purpose to match the game gun. Drill holes for the rivets on one side, the roll the sheet into a circle and rivet together. Once you get the rivets in it should naturally form a perfect-ish cylinder.
Trace the end onto a foam board and cut out three circles to help it hold its shape. One will be put in the front permanently, you can make this one as tight as you want. After you put it in, hot glue it into place from the inside.
The second one will be for the back end, but this one you will take in and out to access the inside of the gun. I made mine slightly big and tapered the edges. After a few fits it started to naturally sit in place. I would recommend putting a single drywall screw in it to pull it out..
The third piece will be for the middle, it will be a little looser and will need to be modified later to get around the backbone. It will be less for holding shape and more for keeping the barrel from deforming too far when the end piece is out. With the end piece out this barrel is very weak, be very careful with it so you don't deform it too much.