I'm not so sure about excessively more expensive. It will be more expensive, but if it costs 5x as much, and is 10x as effective (not to mention needing smaller magazines) then it's still worth it. The only time unguided rounds will be used is when the kill radius is larger or similar in size to the CEP. And that means you need a planet-sized kill radius.
From a few pages back:
Cost of a Sidewinder Missile: ~85k $. Cost of a 80kg chunk of pure Iron: roughly 6k $ (actually a bit less). Foolproof radarguidance seekers are quite probebly 10x the cost of an old IR missile.
Now, let's ignore what else I wrote there and do a proper calculation:
The price of the "Missile" is dependent on several factors of technological advance:
1. It's a bit cheaper due to replacing the explosive with solid metal.
2. The electronics are going to be a LOT more sophisticated, and expensive, as we'll need to miniaturize them; 85kg is too big.
3. Fuel efficiency can be expected to go up drastically, so more space for the above.
Let's assume for now that all of the above +material savings cancel each other out, so the missile would still be around 80k$
4. We need to develop a suitable electromagnetic shielding to prevent the insane Electric field of a Railgun able to accelerate an 8kg projectile to 50+kps in a timeframe measured in nanoseconds.
While this will be food for thought, let's still assume it adds nothing to the cost AND still allows the projectile to actually track anything.
5. With technological advance, production might get streamlined (though we're already basing this off a missile in production for over 50 years), let's reduce the assumed cost by another fourth, which would be roughly 60k $.
After expending it's fuel, the projectile will very likely still have more than 7500 grams of impact weight, a bit less than a solid slug, which would probably be a bit more dense and thus the same railgun could fire a heavier unguided slug, but I'm not too sure about the mechanics, so I'll ignore this altogether, correct me if I make wrong assumptions.
Now, I compare this guided projectile to a simple 8kg slug of iron, or let's use one of the handwavium materials, and assume it's a bit more expensive, like, exactly 600$ for 8 kg (yes, I bend the numbers a bit for easier calculation, but so far not in my favor as far as I can see).
In direct comparison, we can now assume that a guided slug is roughly 100x more expensive than an unguided projectile.
Don't get me wrong here, please, I still think that this would absolutely be worth it, even if it's just 10x more efficient, the higher killspeed and reliability would indeed be worth it in a fleet battle, and one can assume that a single railgun of that size would cost upwards of 10 Millions, maybe more in the range of 50.
However, there's two other paths the thread:
First, for planetary bombardment, I can see that commanders would avoid what essentially amounts to shooting money at the enemy.
Second, the biggest cost factor, and at that calibre also a significant size and low firerate, would be the railgun.
The War Ministry could probably save a lot by building a ship roughly half the size, let it accelerate for a day, and instead fire those projectiles from box launchers;
Which offers the additional benefits of less size restrictions, and less required electronic shielding on the projectile.
I'm not advocating against guided rounds, I'm advocating against railguns for dispensing them in medium range battles.
Other stuff:
@jseah:
Look thorugh this thread for the new armor and nuke mechanic.
Armor will be 1 cm/ layer now, and a 1 ton contact nuke would probably evaporate a capital ship.
Though I'm really looking forward to realistic atmospheric mechanics; While this will mean more weapons can do harm in an earth atmosphere, it will probably also mean that against thinner atmosphere, those weapons will do less;
Also, do planets have a proper size, now that ranges seem to calculated in meters instead of 10000 km?^^
