It seems to use come form of automatic collector scoop to draw in air, which it then compresses in a chamber to drive magazine fed nails at a reasonable velocity (you don't need that much speed to make a nail deadly, unlike wide bullet). Given the tech level of the Fallout universe, I don't see why they couldn't do it.
As a military weapon, it'd be impractical in the same way they are now (just gunpowder propelled rather than air), as they cause very small wounds. Good penetration of armor and retained velocity though.