How can the machines built by Humans fire on Pandora? [duplicate]

All modern ammunition contains its own oxidizer. The components for combustion are present in the materials that make up the propellant-the gunpowder in a shell casing, in a basic example. It's true there is some oxygen in the Pandoran atmosphere but not enough ambiently to feed a really quick powerful explosion that a bullet would need to really get going. The solid fuel of the SRBs that we use to send vehicles into space operate the same way. Liquid propellant rockets contain two separate tanks, one of the fuel and one of oxidizer. Ambient oxygen in the atmosphere is not required, or even more useful. It's a lot more convenient for the oxidizer to be immediately available in the fuel medium.

According to this site there is oxygen in the atmosphere:

Pandora's atmosphere is a mixture of nitrogen, oxygen, carbon dioxide (>18%), xenon (>5.5%), methane, and hydrogen sulfide (>1%) and is about 20% denser than the atmosphere on Earth primarily due to the high percentage of Xenon; a heavy, colourless, odourless, and generally unreactive noble gas. The high concentration of carbon dioxide in the Pandoran atmosphere makes it extremely poisonous to humans

So the atmosphere is toxic because of the carbon dioxide (that is why humans need the mask), but there is also oxygen and therefore the human build weapon can fire.

See also this question and this answer.

I think a bullet already has oxygen in it when it is packed, if you have seen real bullets you will notice that they are packed in a way that air cannot enter the shell, so when the trigger is pulled the gun powder catches fire even before the bullet gets apart from the shell and the reason behind that is that oxygen exists inside the shell, and the second thing is that the atmosphere in Pandora contains oxygen and some other gases that help in burning fire and flames and explosions.