This is the Imperial R-80, nicknamed the "Shipboard Rail-Gun".
Despite having a nickname that implies it's a rail-gun turret, this gun is very portable. With no kick, and half-inch diameter rounds, it's easily the most accurate and destructive weapon in the Imperial Infantry's repetoire.
The most interesting aspect about the gun is the rounds it fires. After exiting the barrel, the round sheds hundreds of layers of diamond shards off of it. The user is safely protected from the rounds, as the diamond comes off about thirty feet away. The rotation of the bullet causes the diamond to fly off, forming a twenty foot diameter cloud of diamond.
Needless to say, the effect of light hitting the individual shards has earned this the second nickname of: "Happy Sparkle Gun", by disillusioned veterans on both sides of the Imperial/Confederate War.
The rounds, though seemingly light and delicate to the touch, are very durable, and can bounce off of metal surfaces reportedly four times before breaking apart. This is a common tactic employed by Imperial soldiers defending cruisers and installations, where a breach of an adjacent wall will cause a huge decompression. Firing around corners to kill boarding soldiers, or clearing a hallway with one shot, are the most common uses of the gun.
Due to the bouncing nature of the bullets, these can be deflected by boarder equipped with solid steel tower shields, back towards the firer. Due to that, Imperial gunnery Sergeants instruct the users of these guns to aim at the ceilings above the target, to avoid the shields, or any bulkheads covering the walls.