okay to start off i have tried all sorts of ways no make a marshmellow gun automatic and without costom makeing some sort of spring action thing in a machine shop i don't think there is a way. but heres a nice way to achieve simi auto-ness. now your probably going to say "well what aboutthis ? well thats closer to a shotgun dont you think?
Step 1: What You Will Need
i have got two models one being the the rifle (in my opinion it works the best) and the submachine gun
heres what you need for a rifle ( all of this is 1\2 inch schedule 40 unless i say otherwise of course)
1 45 degree
about a 1 1\2' schedule 40 and the hopper is schedule 20 (more space in the pipe so the marshmallow can slid down) doesn't matter how long.
somthing to make holes in schedule 20 pvc pipe (like a power drill) hole cant be too big (see the pic)
wire to match the hole you made in the pipe (see the pic as well (that black thing sticking out of the hole)) you will need a whole ton of it believe me it gets used up quick (about 3 feet)
and of course mini marsh mellows.
Step 2: Assemble
the proportions are not a big deal just look at the pic thats the rough design. i also have the sub machine gun down there if your interested.
Step 3: The Mag
all righty now make holes about 3\4s of an inch apart through both sides (obviously). now cut the wire in to 2 1\2 inch segments. now its done. make sure you leave a gap of holes for the cap on the end and the tee piece on the gun at the bottom.
Step 4: Loading and Firing the Gun
fit the mag into the gun and slip one of your wire segments in to the closest hole to the bottom (the bottom being the end in the gun) then drop a marshmellow down the mag at the top then slip another wire in at the hole above the marshmello and slid another marshmello in do this untill you reached the top and put the cap on now remove the bottom wire and the marshmellow will fall into the gun and you can blow (try to make it a quick burst of air) then the 2nd wire then the third and so on. as you will see it jams somtime but a lot less i can assure you then if you had no wires at all. and thats it.