Step 3: Barrel
PIC 1-2: build this part (it is the front of the barrel) PC 2 is of the same part upside down
PIC 3-4: build this. It is the middle part of the barrel.
PIC 5-6: build . This is the back part of the barrel and the firing mech
If you can't follow any of this Instructable let me know on my orange board and I'll try to help.