This barrel is pretty similar to other barrels but to let you know, if you do not have enough little metallic blue pieces you can replace them with beige connectors that have 2 blue spacers in them.
Step 2: Make handle
This is the handle of the sniper rifle with a slight modification.
Step 3: Make firing pin
This is the firing pin and it has a hand attached to it for the pump action goodness.
Step 4: Make clip
This is where you put the blue pieces to fire.
Step 5: Assemble
Put the parts together in this order, sorry for the blurry pictures but my camera is not equipped for up close photos.
Step 6: Fire!
To fire, pull the front handle back until the firing pin is locked into place and then push it all the way forward. Then, with your index finger pull down on the grey piece to the right of the rear handle.