What you are making is more than likely just an arial pyrotechnic device... same thing as you can buy at the fireworks store in many states.
There is a max limit on the bursting charge to be legal. I havn't looked at the pyro sites lately, so I don't recall the numbers. However, if you are launching a firework that you can legally buy in the US, you are more than likley under that legal limit.
For instance, you can not buy M-80's which I believe contained 80 grains of flash powder. If you got caught with one, you would have in your possession a very illegal thing... can't launch it, cant have it. M-50's and smaller are treated differently.
I'm not a lawyer, do not take what I just said as legal advice. Instead, look at the legal warnings on the big pyro sites (skylighter, pyrocreations, Foxfire, etc and see what they are saying. The last time I looked there they gave references to ATF regulations, so check those out too.
Currently, the pyro dealers are going out of their way to give you good advice to help keep you legal, because they are all under legal attack by the Consumer Protection Agency. As a side note, Foxfire is in court with a pending compromise ruling due any day now (overdue in fact) that may affect not only hobby fireworks makers, but cannon shooters as well.
You can launch pyrotechnic devices out of a launcher tube (they call the tubes "mortars" too). There is just a max limit on the payload bursting charge chemical content. Check out the pyro web sites and the ATF references they contain and stay on the safer side of legal.
