To accessorize my Son's Halo costume:

https://www.instructables.com/id/Cardboard_Halo_3_Master_Chief_Helmet

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

I used a scale drawing and other reference pictures I found on the internet to get the general shape and size of the weapon. The 48" length was determined to be the best size for my Son's height. I drew a grid on the side view of the diagram and used it to transfer the silhouette to the cardboard. I made two sides and glued the inner and middle tubes and scraps of a wooden handle to add support to the structure.

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 scope tube was made from two 1-1/2" PVC couplers. The two together proved to be too long so I cut one of them in half.

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

I found a paint/stain applicator for about $6 on clearance for use as the bi-pod. It was simply insterted through a hole cut into the body. Hot glue and a dowel rod holds it in place.

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 final step was to install the sound chip (from Radio Shack - $11). My Son helped me find a suitable sound of a rifle firing on the internet. We recorded it and the chip was installed in the handle under a piece of cardboard where he simply presses on the cardboard to activate the button underneath.

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.