What super-dense solid could be produced in large quantities using only Earth's atmosphere?

Assuming the power and tech existed to do so (addressing the requisite heat, pressure, etc), would it be possible to draw in atmosphere, condense and heat/cool the particles, and then produce a highly-dense solid in large quantities?

For example, could my imaginary (and admittedly SciFi heavy) machine be the size of a backpack and draws in surrounding air, filters out whatever elements are needed, and then cool/collapse the particles until they form the desired solid, creating ammunition? The backpack creates a specific caliber round -- say 9mm/120gr in size -- and feeds it into a gun to fire via some delivery mechanism -- likely coilgun in nature. The backpack doesn't store the ammo.

If this is theoretically possible, what super-dense solid could be produced in large quantities using only Earth's atmosphere?

Note: I've read through multiple questions relating to compressing air to form a solid and wanted to dive in deeper into the options -- ie not just O2, but nitrogen, CO2, etc.

posted about 4 years ago

TIM FENNER‭

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