1. Forex (cardboard like material).
2. Plastic caps.
3. Aluminium pipe as barrel.
4. Square metal pipe as holder/carrier(which is welded in L-shape inside & fixed in a ply-wood).
5. Ply wood( as a base for barrel and body).
6. Any cheap airsoft gun's handle(gives a perfect look).
7. A small can or any similar sized plastic bottle as a grenade reloader.
8. metallic nuts and volts or rings to give some finishing touch.
This can be best use as a sci-fi prop gun. Or a collection gun. Or as a decorative piece on your wall.
The video is not so good since i am new to after effects, you may add muzzle flashes and smoke effects with the gun or simple lasers lights to make it as a futuristic prototype gun.