To save this I put this as part two: Why I hate (most) ammo in a space game (hopefully shorter):
Like fuel I imagine a universal renewable energy (that defies newtons laws, which is possible; newton has been wrong before) that powers engines guns, and the ship's electric generators (like a car.) If not renewable than is a 24,000 year nuclear battery okay (+1 to whoever first guesses which nuclear fuel has about this long of a viable life.)
I said most cases because I believe ordinance (bombs, missiles, torpedos, ect.) should be limited and had to be purchased. While anything energy should be generated.
I don't believe in space ammo mostly because it sound's ineffective. Looking at current bullets, the only thing I would even think about aiming at a battle ship would be a 50 calibre (hint not a mini-gun, an HMG) and that probably wouldn't penetrate a fully armored battleship. Now looking lets be generous and say an average shield negates 25 percent momentum from an average bullet. A battleship of today has a lot more than 75 milimeter armor plating, so if we took a futuristic alloy with twice as much plating for your average space battleship, your most powerful NATO round wouldn't dent it, maybe ap round would scratch it. So let's take an unconventional bullet, an elephant round 100 calibre, maybe this round would break halfway through, or maybe three quarters realistically. Problem is, an standard 50 calibre cost 4 dollars around. Let's guve credits a very generous 2.5 inflation. So 10 credits for a 50 cal. Elephant round is twice as big so it is 25. A general encounter sees around say 10,000 rounds in a large ship fight (one side) that is actually not a lot of bullets, about 100 HMG belts. That is already 250,000 credits. After a more realistic fight you are more likely to pay 2,500,000 to restock. That is only 100,000 rounds. That means to not micromanage you need to stock by the millions. Obviously to by 1 or 10 million round you will have to pay 25 or 250 million respectively. It's a lose-lose, you either pay all your hard earned credits or micromanage rounds.
I've probably gone too realistic for what ammo in-game would look like. But ammo is realistic limiting for me anyways