Black powder guns are not federally controlled and can be shipped by mail to you. There are a few places (mostly major cities that do restrict black powder, it is always best to check with local law enforcement first. You don't need a yard full of black suburbans and guys in jumpsuits.
Black Powder.
Assuming you are of legal age to purchase, black powder or smokeless powder for reloading can be purchased from gun shops. Yes, proof of age is required.
To the best of my knowledge unless you are a convicted felon you can own a black powder gun.
Yes, a black powder gun is considered a firearm under federal law.
Chinese
I imagine state laws vary on this but in Texas you do not have to call anybody to transfer a black powder gun.
Upon installing the cylinder you have, according to the law (or at least the ATF), manufactured a firearm. So the simple answer is "No". It is not legal for a felon to own a firearm (gun) and once you install a conversion cylinder that pistol is no longer a "non-gun" black powder pistol.
no rockets run on black powder (gun powder)
who made the gun. how do you know it's a black powder gun ????
Spain
Charcoal and saltpeter (if you mean black powder)
Black powder, or a black powder substitute such as Pyrodex. Smokeless powder (modern gun powder) should not be used in a traditional muzzle loading firearm.