This high-powered, recoiless slugthrower can be fired in short bursts to devastating effect, although the sizes of its housing and power supply require it to be mounted on a MEC. Prior to our research on heavy lasers, we had no access to a small enough power source.
Real-life railgun development is indeed hampered by inadequate materials, bulky power sources, extreme heat build-up, and can burn their rails to the point of uselessness in one shot.
There is significant debate whether the term "recoiless" is applicable to this weapon. A kinetic weapon (like a railgun) generates recoil by default due to Newton's Third Law of Motion in proportion with the energy of the projectile; conventional recoilless weapon designs (such as the Rocket Launcher) rely on some form of counterforce, usually a jet of flame, released from the back of the weapon, to counter (most of) the recoil. The Railgun instead has a solid butt-plate, in stark contrast with the less conventional interfaces of both the Minigun and the Particle Cannon, and is carried by a super-strong cybersuit that fires it in single shots only while solidly shouldered, while still visibly struggling with the recoil.
An open barrel with unconnected rails is a possible design weakness - rails repel violently during firing.
The Railgun is one of XCOM's three advanced projectile weapons; the others are the chemical Phoenix Cannon and the magnetic Alloy Cannon.