You can make a strong blow dart by coiling metal and attaching some matting material for the tail. You can paint the tail to finish it off. These are not toys but are made out of metal so check if blow darts are legal in your state.
How to make blowdarts out of some cotton and wire, These are actually a bit better for larger diameter blowguns, the ones Im making are for 3/4" ID blow guns. The result of over a year of Trial and error. These things pack quite a punch. You can expect to easily penitrate thin metal, such as spray bottles, pop cans, and even the rain gutters on the side of your house.
These darts arnt the prettiest things, But they do their job well, and they wont fall apart on you, So the only thing you have to worry about is not losing them. They unfortunatly arn't the quickest darts to make.
I mention in the video, but these make pretty sweet target darts, But i suggest getting a piece of particle board to shoot at. You know, paint a target on it or whatever :p
And For thoes of you who dont already have one, Im planning a 'How to make a Totally Awesome Blowgun' video next. These things are cheap you can spend as little as $1.50 for a pretty sweet gun.
Im also considering putting up a video for my High performance blowdart design.
LEGAL: Blowdarts are Illigal in some places, Including Canada, The UK, California, and Massachusetts. So make sure you check your local laws.
Ontop of that, a blowdart is a deadly weapon, Dont shoot where you cant see, dont shoot up, dont shoot when there are people or animals downrange ETC, Basicly treat it the same as you would any other gun.