the design for this instructable is fairly simple.
All you need is a cap for an airsoft bb bottle, a pen or straw, hot glue gun, electric tape and the nerf titan as-v.1.
Step 1: 1
first take the pen apart and keep the tube. glue the small part of the cap to the tube or straw. to mak it air tight use the electric tape. Not rocket science.
Step 2: 2
now hot glue the bigger end of the cap to the end of the barrel. now tape and hot glue the crap out of it make sure once again that it is air tight.