This is about all the pieces you'll need. which would be couple pieces of wood,plexi glass,screws,a spring,bungee cord,a rubber band, a exercise band. Also the tools you would also need would consist of a hammer,drill,a vice grip,a band saw.
Cut the wood to the shape of the gun which will ultimately be 1st layer of the gun. so what you would want is the handle and the base.
so after you have made the shape of the gun make an identical base which would be the middle of the gun,but dont attach anything yet because you will need to cut some off
make sure that there is two inches between each barrel so i did the model on google sketch up so that my measurements would be on point
so after you do that last step get a piece of plexi glass if your able to try to trace the shape of the gun so that it is equal in size and length
so after you trace the shape, cut it out on a band saw and line it up to the gun.if there are a couple of rough edges dont worry about it we'll be able to sand it down. so after you've figured thats the way you want it pre-drill a couple of holes so that it is alot easier to drill the screws into the oreo despenser. sand it down after it is completely even sand down the edges for a nice clean look.
so next thing you want to do is cut a notch in the middle of the second barrel reaching all the way to the trigger
the next thing you would need to do is the pump. to do this all you need to do is measure the bottom of the despenser give it a little more room than you would need so that the side walls are close to the sides of the despenser
so after that get a piece of wood and cut it so it kinda looks like the front of a crossbow. after this drill two holes on each side of the piece you just cut out cause thats where the resistance exercise bands will go. after you drill the hole, cut the resistance band in the middle so that its perfectly even, pull the resistance band through the holes tie a knot on the side your pulling through.
so after all this the next thing is to make the spring loader. cut out a piece so that it looks kinda like a ramp place it in the despenser where the spring is make sure there is enough room in the notch that was previously cut. and your done just make sure that the length of the sides that stick out from the pump reach all the way to the back