Railgun

Features
A Railgun uses magnetic rails to fire solid chunks of matter, called slugs, at near light speeds. They are incredibly accurate at long range and the damage they inflict depends on the mass and the speed. The more massive and the faster the slug, the more devastating and difficult to avoid the hit will be. In theory they can inflict any amount of damage, penetrate any armor and possibly explode.

The energy stored in a slug follows the formula

$$E=\frac{m_0 c^2}{\sqrt{1-\frac{v^2}{c^2}}}$$

where m0 is the rest mass and c is the speed of light in empty space. For v getting close to c this is a divergent function.

The limitation is that the magnetic rails must provide the energy to the slugs and have to deal with issues such as rail length, electromagnetic shock absorption, heat dispersion, nonlinear superconductive response and chaotic path divergence. Technical solutions to these problems are abundant and can completely change the properties of the Railgun.

Typologies
Any chunk of matter that contains magnetic material can be fired. The higher the percentage of magnetic material, the higher acceleration the slug will be subject to. This allows a great features of design, each with specific technical issues.

Notable types are the following.
 * Metallic slug: easy to manifacture and uncomplicated to handle, they can be fired in great number and have a very high speed. They damage the enemy ship by breaching their hull. A sub-type is the frag-slug that will shatter on impact inflicting a reduced damage on a bigger area.
 * Bio-slug: a metallic slug enriched with bioactive substance. Provided that the slug penetrates the hull, the size of the shock wave will also contaminate the area with poisonous or dangerous organic agents (such as neurotoxines or viruses), killing additional crewmembers and complicating repairs.
 * Anti-slug: a slug that uses the explosive power of antimatter. Most designs resemble propulsionless torpedos (a metallic hull with an antimatter core in a containement field), have very high detonative potential and can't auto-target or change trajectory. There are rumors of slugs made 100% of antimatter, although the technical problems are very high (they would require the ability to manifactur anti-iron or similar heavy elements); nevertheless it is agreed that a quasi-transcendent species could have them and the space-pubs of the Triangulum Galaxy are filled with space-traders ready to swear that they once dodged one of those.
 * Hardcore slug: at times nicknamed diamond slug, it is an extremely sharp projectile. They are usually made of some extremely hard material (diamond single-crystal being the prototypical one, although it is not adviced due to poor resistence to heath) which allows them to pierce through the staship instead of damage the hull. Hardcore slugs have been known to travel the starship side-to-side, which also means that a well-aimed slug can for example destroy the warpcore and annihilate a starship in one hit.

As a rule, metallic slugs are the fastest and their blunt force is useful in all situations. Bio-slugs sacrifice some of that force but can have long-lasting effects and possibly kill the whole enemy crew. Anti-slugs are not unlike torpedos and have the highest detonation power. Hardcore slugs are the only one able to penetrate deep into the enemy ship, but they tend to be much slower.