[quote=Goldmarble]
I do believe you are missing the point:The oxygen for the reaction is contained within the powder itself. The reaction does not rely on oxygen in the atmosphere at all. If it tried to? It wouldn't work, because there is not enough volume in a cartridge case for both sufficient powder, AND air, to operate at the same efficiency.
[/quote]

Well technically 'oxidizing agent,' typically saltpetre, which contains the element Oxygen in a nitrous molecule.