why would any of the stations have firearms on board? Or were they maybe manufactured (printed/ fabricated on Mecha?) after Unity Day due to issues like famine and riot? Still though, firing a projectile in a space startion is a risky business which could easily casue depressurization. And why did any station have nukes or any type of defensive/offenisive station to station weapons? This is pretty much a per peeve of mine and is minor I know, but it kind of 'sticks". Similar too, why would the Eligius Compamny so heavily arm their mining ships? Its not just small arms, they seem to have some heavier machine guns as well.
I would say that the firearms were manufactured after Unity Day, maybe due to famine and riot, something we know happened on the Ark with the 'Blight Generation' who resorted to canabilism with the dead bodies.
Since we can already 3D print various things in 2018, though I am not entirely sure as to the current limit, we can assume that when the Ark was formed in 2050's, they could fabricate and print a variety of things that we cannot do today, and seeing that there are already prototypes and models of 3D printed weaponry, primarily guns, we can assume those on the Ark can. I say assume as they would need a 3D Printer/Fabricator upon one of the Space Stations prior to the merge of all space stations, as well as the materials needed.
For firing a projectile and causing depressurization, we can assume that since the Ark is in orbit above the Earth where there are thousands on bits of metals the size of bullets from sattlelites and rockets sent into space, they would of created some kind of glass in which can stop the bits of metal, bits of metal that travel a lot faster than bullets can. This is to say that the governments of 2050 haven't 'cleaned up' orbit of all the pieces of metal floating around. Either way, materials used would have improved alot since today, since the creation of the Ark is in the 50's, 2050 that is.
The offensive and defensive weapons would probably be the same as putting weapons on the border of a country, since offense from the space stations would cause damage to the country that was hit, while an offense from a country on the ground on a space station would result in debri and possible nuclear fallout, should they use nukes, to be spread across the globe. More of a deterent than anything else.
For the Eligius Company, I have never watched Season 5, so I cannot say much. I have read some of the plot and information as to what happen's but not enough. From what I can gather, the prisoner's were used to mine an asteroid. When I think of this, I think of prison's in the 20th century which would use prisoners for hard labour, though some still exist, though due to it being an asteroid, it can be assumed that the drill would be part of the ship, not prisoner's having to mine it manually. The Eligius Company is a bad plot altogether, though the person 'in charge', Jason something, is basically just dragging the plot along now. While the Grounders and Mt Weather seem a more reasonable outcome of a nuclear apocalypse, somewhat, the rest turned really bad, with the exception of the A.L.I.E, which was weird on all counts.
The really bad include the Second Dawn Bunker and the history, with burning Becca on a stake, and how the Grounder saying's are sayings from the Second Dawn Bunker with the crazy Bill Cadogan, people who are in Egypt which we see in a scene, slaves at Farm Station, the story ark of Illan, the Final Conclave and Wonkru (Which makes me think of Ron Weasley as Lavander Brown calls him Won Won), The Dark Year where the Wonkru resort to Canabilism, Everything to do with Wonkru, flashbacks with the flame in Madi, Harper dies of a genetic Condition, which is basically a way to get rid of both Harper and Monty, and now a whole new planet, where there will be some sort of issue where people cannot work together, or there is already natural life there.
The firearms were probably on the Ark for security purposes or for protection once the Sky People have gone back to Earth. When guards are seen on the Ark, they only have batons and electro batons. They never carrier guns. But when Alpha station crashed and Camp Jaha was formed, all the vuard members and Chancellor Kane had guns and holsters on them. They were probably manufactured on the Ark by Factory or Mecha Stations. But they could have also been there since the all 12 stations joined to formthe Ark. The purposes of the 12 national stations is never mentioned. They could have been for science and research. But they could have also been for orbital bombardment missles built by countries. As seen on the first Unity Day, Alpha Station (former United States National Station) fires a missles on Polaris Station. Also in season two, Jaha boards a missle to come to Earth. Obviously space reasaerch organizations dont need missles and warheads.