This question has options. How would someone go about accomplishing this goal?
How to glue together your cardboard sniper rifles?

OPT: I. Cut "filler pieces" or cardboard squares smaller than your rifle hand pieces to fit in the middle. Glue a border around the handle. Cut out a long strip of cardboard the same width as the handle and glue it to the pieces. II. Cut "filler pieces" or cardboard squares bigger than your rifle hand pieces to fit in the middle. Glue a border around the handle. Cut out a long strip of cardboard the same width as the handle and glue it to the pieces.
I.