You don't need any oxygen in the casing whatsoever. All gunpowders contain their own oxidizers: potassium nitrate in the case of the long obsolete blackpowder, and more modern smokeless powders are all nitrated compounds, usually the majority being nitrocellulose.
You don't need any oxygen in the casing whatsoever. All gunpowders contain their own oxidizers: potassium nitrate in the case of the long obsolete blackpowder, and more modern smokeless powders are all nitrated compounds, usually the majority being nitrocellulose.