This is something that i use to make when i was little. Thought i would share with everyone. There is one out there almost like mine but you don't need to cut anything on my design. All you need is 2 pieces of paper and a pencil or something round.
Get one of the 2 papers and roll it up with a pencil.
after it is all rolled up you have to let the paper loose just a little bit so the pencil can fall out. Then fold it in half.
Now you flatten the rolled up paper and set it aside for later. Fold the other piece of paper in thirds on the short side so it stays 11 inches long. Fold the paper again in half this time so it stays 11 inches long but a few inches wide. Then fold it in half this time so it is 5 and a half inches long.
Put the flattened tube inside the folded paper. pull one end of the folded paper through the flattened tube. then pull the other end of the folded paper through the flattened tube and pull both ends tight. you can color the gun if you want or use different color paper to look different. or what my son like is if you put two of them together with the end of the barrel inside the back of the other gun it kind of looks like a machine gun.