I worked in the Museum of Natural Science this summer and wanted to have some fun with my students. I looked up online and found marshmallow shooters, specifically on this site. I liked the designs, but felt that the kids would get bored and I wanted the making of the guns and following "war" to be really entertaining and take a couple of days to complete... so I sat down and invented a rifle any kid would love. Attached is what I finally came up with, along with simpler and cheaper versions. The last is what I found on this site. As for how to use... Like I told most of the kids I worked with... It is like trying to get a hair off the tip of your tongue without using your hands, or playing a trumpet... Try it and you will be launching mini marshmallows at least 100 feet with this rifle!
Good luck and good hunting!