525um Convetional Gun

So there is no reason to use bore radius lesser than 10mm? ;_;

Wider projectiles are better mainly due to the game lacking the ability to have a wider chamber than barrel. Since you generally want to have a lot of propellant compared to your projectile volume, you'll have to waste a lot of barrel length for just storing the propellant. When shooting CD discs this is less of an issue: you still have a lot more barrel length used by propellant than the projectile, but since the projectile is so thin it doesn't matter as much.

Another issue is that a thin, long bunch of projectile burns longer than a short, wide one, which means that for the same load you need a far longer barrel and are affected more by beam deflection stress, meaning your barrel has to be stronger too. It still doesn't mean you can't have guns that fire non-disc projectiles, you're just limited to lower muzzle velocities or ridiculously heavy barrels if you want to go higher.

Below is a comparison between wide and long projectiles with an identical propellant load. The wider projectile cannon is 3 times lighter, the barrel is far more aesthetic, and it gets a higher muzzle velocity.


When it comes to propellants, the differences are fairly minor. It's mostly a tradeoff between mass and cost of the propellant, although with Octogen and Cyclogen you can get a bit higher muzzle velocities than the cheaper ones. I mainly use either Octogen for a lighter, high-performing propellant, or Nitrocellulose if I need a dirt-cheap option where performance and mass are not that important. Since TNT and Nitrocellulose put out less energy per kg but are cheaper, they'll be far cheaper to use than the better propellants, but you'll usually also need a heavier barrel due to their slower burn rate.

Propellant choice also affects how your breech pressure behaves. Octogen and Cyclogen burn far faster than the cheap propellants, which means that you'll need a stronger barrel but since pressure tapers off more quickly, your barrel can be shorter. VCS is usually a good barrel material for these propellants, since it has the best strength vs mass and cost if you need a short barrel. With VCS your barrel is also usually quite thin, which means it looks nicer.

With the slower-burning TNT and Nitrocellulose, your pressure curve won't peak so high but it also takes longer to taper off. You'll usually want a longer but softer barrel here, which means you'll want something lighter than VCS. Good choices here are Amorphous Carbon, or perhaps Titanium if you think carbon-based barrels are questionable. The weaker material will be a lot cheaper than a similar VCS barrel but you'll lose out some credits to your turret momentum wheels, since the longer barrel will have more moment of inertia to overcome.

Below is a comparison between the different propellants with an identical barrel and projectile. You can get very similar performance out of all four, but note how the pressure curve as well as mass and cost of the full cannon+ammo assembly changes.

Pretty sure it was the inverse.

aerogel is better for stiffining and diamond is better for heat issues

But diamond has higher young's modulus than the aerogel which makes the diamond a better chooce for stiffining?

Yes.

Just that less pressure equals less acceleration and that’s wasteful.