These are really stupid, but if you are really bored it will give you something to do. One good thing about them is if you make them right and use green fuse, they will go off underwater. Just make sure to tape them to a rock or something because they float. Just get an empty .22 shell, fill it with powder, stick a fuse in it, and crimp it over with needle nose pliers. They aren't any louder than a firecracker, but the "homemade factor" makes them more fun. The only near-difficult thing is getting it bent over right. If it isn't bent well, it wont be very good. This picture shows what they should look like.
.22 Magnum (they are longer than normal .22's are the only ones that work. regular .22's are too short. You can also use larger cases like .223, .44 or any other long casing.