My version will work and fire small balls of tape etc from a smaller shotgun style carriage inside the ammo barrel,using extreme small amounts of low power propellant,might even try lighter/barbecue fluid,BP in super tiny amounts etc...or alternatively just use it as a prop.
I'am not responsable for however you use this crazy creation and it is by no means safe,unless used as a prop that is.
Step 1: Tools needed and early Construction.
How to start off:First cut your two sections of PVC pipe/tube to the desired side requirements,thats the simple part now making the stock cut out your templates from thick card x2 and parts for the bottom and top of the stock,glue it all in place as shown,tricky part making the bracket/brace to fix the barrels in place, make one small and medium card box open ended that the tubes will fit into and slot into check it as you make or build around the tube as i did so its exactly the size needed now lengthen it with more pieces of card,glue this thing with a large amount of glue,now the last part here the smaller barrel as pictured affix card end piece stopper with a hold cut in for the wires to go in much much later i added straws for optional led power light at much later date or not at all,in case your wondering why the hell there straw pieces in there,now the main parts have be made to create the body..onto assembly.
Step 2: Finishing off construction.
Check it all slots together as shown in the pictures,once you're happy its a nice fit,glue the smaller piece barrel to the bracket piece not the longer barrel but the the bit that will affix it pretty simple,now glue on the stock to the smaller barrel as shown and apply a hell of alot of glue to it and let dry for a number or hours before painting your desired color scheme,went for blood red and left the barrels black.
Last few pictures here show the internal heat shielding part created simple from aluminum drinks can,foil and other wadding will be added when firing this,as seen there is a gap at the handle of the stock for a push switch to be emplaced and a moveable slot on the underside for adding a battery pack and any lose wiring.