To make a bigger explosion you need a bigger barrel and more powder charges.

Eventually you hit a limit where you simply can’t create enough pressure to propel the projectile faster and not turn the barrel into a pipe bomb.

For the most part many guns have already hit their practical limit in this regard.

There is a good reason why battleships fell out of favor other than the US being the only blue water navy after WW2.

Those big guns are a bitch they are slow to reload and you can’t be anywhere near the muzzle including good couple 100 yards of the bow of the ship when those fire.

Also powder takes up space and weight, takes time to reload and it can explode when ignited.

Having a gun with parts that don’t explode intrinsically when set on fire is a pretty big advantage for any combat vehicle or vessel, not needing to carry propellant for your rounds is also a huge plus because you can carry more rounds or other munitions and supplies.

It isn't only that, with a powder charge you are pushing the projectile with an explosion. That explosion will also cause a disturbance on a ship, until you get to a pretty enormous size, you have to calculate that into your trajectories. With a railgun, you have a series of magnets pulling a projectile forward incrementally faster. It's a lot less energy wasted into the environment, meaning a lot less energy put back into the ship. These larger guns could be put on smaller ships and calculated with greater accuracy with greater ease due to less wasted energy put back into the ship and gun, I'm guessing.

What you are describing is a coilgun, a railgun uses a slightly different principle.

Oh. Ok, I'll have to look into that. New project to look into for the summer =)

You are describing a coilgun.

> the US being the only blue water navy after WW2

The UK projected and fought a conventional blue-water naval war in the 80s.

The real reason battleships fell out of favor is that aircraft (and eventually missiles) are better at basically everything.

Explosives are really dangerous to carry around. Go looking through the fates of ships lost in WWI and II (last time there was a fair amount of ship combat going on) and there's an awful lot of "several rounds hit but everything was basically fine, except then one hit the magazine, blowing the ship in two and sinking her", or a fire starting and doing something similar, or a smaller cache of explosives readied for immediate use in a gun blowing up and causing massive damage, or whatever.

Not sure if that's the reason, but it's probably a reason.

It wasn't even shells hitting magazines. It was shells hitting gun turrets, with the explosions reaching the magazines.

In the Battle of Jutland (The largest naval battle of WWI), the Royal Navy lost three capital ships (Two battlecruisers and a heavy cruiser) to single shells that struck their gun turrets, detonating their ammo magazines.

The gun turrets were, in theory, supposed to be sealed off, by blast doors, from their magazines - but in order to increase fire rates, it was standard practice to leave those doors open in combat.

The Germans, not being suicidal lunatics, kept equivalent blast doors closed, which is why none of their capital ships went up in flames, despite taking a lot more damage.

As an addendum:

The Royal Navy had a long and well-established tradition of exceptionally well-drilled gun crews, probably going back almost 150 years from WWI through the Napoleonic era. It could be argued that their fast-firing and disciplined gunnery were decisive in more than one British victory.

HOWEVER....as you point out this led to objectively-suicidal practices....What's that term for when you've been doing a risky job for so long you don't realize how dangerous your habits are? Yeah Royal Navy gunnery is a textbook example of that.

Gas pressure just can't linearly accelerate something as efficiently as magnetic force can. You can get so much more velocity for the same barrel diameter instead of scaling barrel diameter and thickness because you have thrust being added through the whole length of the barrel instead of gas pressure being used to propel a slug at the end and then dissipating.

Yep, this is really a "why not both?" scenario.

Chemical propellant in first stage, electromagnetic acceleration in the second stage.

I'm curious if they want plasma projectiles explicitly, but I guess it's all kinetic at the end of the day.

Germans already took conventional artillery to its limits:

https://en.m.wikipedia.org/wiki/Schwerer_Gustav

https://en.m.wikipedia.org/wiki/V-3_cannon

Space.

The propellant for a large shell takes up more space than the shell it fires, it's tremendously dangerous to have around from both accidents and enemy impacts.

Compared with a rail gun which is room full of exquisitely machined inert metal blocks.

Cost - Those inert machined metal blocks are cheap in a military if not absolute sense.

Though, this only really makes sense on a nuclear-powered ship. You've got to store your energy somehow, and I'm sure gunpowder is less energy-dense than diesel fuel, but from what I've read one of the big attractions of electric weapons is that you can replace all that chemical energy storage with far, far denser nuclear energy.