I built a sniper rifle. It is made from cardboard, scrap wood, PVC pipe couplers and a telescoping pool skimmer pole - available for about $12 online (I had one left over from a blow-up pool we no longer had). It is 48" long and has a module to add a rifle shot sound. It took about six hours to build.
Step 1: Body and barrels
The telescoping handle had three sections. The inner was used for the lower barrel. The inner section extends out to be the 'appropriate' length and the remaining length simply adds support to the gun within the cardboard.
Side detail was added with another layer of cardboard as shown in the fourth picture. Strips of cardboard were then glued between the two sides to finish the gun's structure.
The last picture shows some extra detail and how it looks with primer on it.
Step 2: Scope and Flash Suppressor
The body was made from cardbard and in the same way you make model airplane wings. I cut some ribs and then simply built up cardboard sheeting around it. I also found a plastic piece off an office chair that gave me on of the rounded sides.
To hold the scope tube to the body I created what looks like an extruded plus sign. This was made from three pieces of cardboard and runs the full length of the PVC couplers and the body of the scope. It gave it a lot of support.
The flash suppressor was build up as shown in the last two pictures.
Step 3: Bi-pod, Barrel Detail and Scope Installation
Two 2-1/2" PVC couplers were glued together and slipped over the main barrel. It was covered with some cardboard with notches in the middle to give it the appropriate detail. Cardboard was cut and glued to the ends in cones to finish it off.
Extra cardboard detail was added to the scope and it was attached to the top of the gun on a cardboard base.
Step 4: Sound Chip
The record button, microphone, battery and speaker wires were extended by soldering lengths of wire and insulating the connections using shrink tubing. These were hidden inside the body of the weapon along. The battery was hidden in the magazine which slides into the body and is held in place with a couple of lengths of bamboo skewers used as pins. The speaker was glued into the front of the scope and a piece of cardboard was glued over it to protect it.
The last photo shows my Son wielding the sniper rifle in full costume - ready to take on the Covenant.