Putting it in a clear plastic baggie magically makes it safe:

Mind you, I had packed the stuff safely. It was in three separate jars: one of charcoal, one of sulphur, and one of saltpetre (potassium nitrate). Each jar was labeled: Charcoal, Sulphur, Saltpetre. I had also thoroughly wet down each powder with tap water. No ignition was possible. As a good citizen, I had packed the resulting pastes into a quart-sized "3-1-1" plastic bag, along with my shampoo and hand cream. This bag I took out of my messenger bag and put on top of my bin of belongings, turned so that the labels were easy for the TSA inspector to read.

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You didn't bring on gunpowder. You brought on wet charcoal, sulphur, and potassium nitrate. You would have to mix the chemicals in the right proportions and then either mix them together with boiling water, spread it thin, let it dry and grind it or spend several hours grinding the contents in a ball mill. Then what do you have? Powder that by itself is fairly harmless. Light gunpowder by itself and all you get is a flash, but nothing that would bring down a plane. What you would need is a casing that would contain the chemical reaction (burn) until the pressure was high enough to cause an explosion of the case. Good luck with that!