In the far future of sunshine and rainbows, the Dark Eldar mastered a weapon cruel even for this setting. A Splinter weapon is what happens when you take the Shuriken weapon technology of the Eldar but replace the standard plasti-crystal ammunition block with a crystallized block of potent toxin.
The difference between the two weapons is that the projectiles fired from Splinter Weapons lack the size to deal damage on their own; they act as vessels that puncture armor so that the poisons can do their gruesome work. This means that while they are highly effective against even the largest monsters they are unable to damage tanks and reliably penetrate power-armored targets, forcing the necessity of other weapons to deal with armored targets. They leave the target with a face distorted into an agonised grimace like an even more fucked up version of Joker venom. It has yet to be decided whether Splinter Weapons of Duke Sliscus' Corsairs; the Sky Serpents, fire conventional Splinter Ammunition or crystallized manly tears wept by their previous foes.
Also, because of the Dark Eldar's need to cause maximum pain in combat, infantry-carried splinter weapons are normally fitted with a number of blades. So basically, their guns are choppy shootas that shoot choppy dakka. Fluff details that the Dark Eldar have running contests to create even more fucked-up toxins to crystallize into ammunition, the better to cause a number of interesting effects on those they gun down. Interestingly, the Dark Eldar do have antitoxins for their own weapons, but most Dark Eldar consider it a point of pride to not use them. It's also quite likely they'd be dead before it could be administered, but whatever.
Like with a lot of things, the fluff is a little inconsistent with how they exactly work. The guns typically have variable velocity settings, although any Dark Eldar worth their spikes will dial down the speed to low enough to be silent whilst attacking, only turning it up when they are pinned down or discovered, which they try not to do.
Ah yes, the infamous dickhead gun.
The Tormentor Helm is the name of the helmet worn by Incubi warriors, and by god is this thing silly. The helms are easily recognisable by the scorpion tail-like gun protruding from the top of the helmet. Unfortunately for the poor wearer, the gun looks like an oversized flaccid penis. Who in GW though THAT was a good design choice, we have no idea.
Anyways, the gun is actually a miniaturised Splinter Pistol, allowing the Incubi some form of ranged attack, as well as allowing for increased ability in melee combat. While the gun functions the same as a normal Splinter Pistol, the method with which the gun is fired has been replaced by a neural sensor embedded in the helmet. This sensor monitors the thoughts of the user and triggers the firing of the weapon once the command is thought. This allows for completely hands-free operation of the Incubus's firearm, a necessary development due to the sect's focus on assaulting using their infamous Punishers.
There used to be models for this thing, but in a rare sign of GW having a conscience, it was removed in 5th Edition. Not even the Matt Ward-era of baby carriers and flying psychic dreadnoughts thought this was a good design.
Tl;dr, this thing is basically the Dark Eldar version of the Striking Scorpion's Mandiblaster. They both function the same in similar roles, with the main difference being the Mandiblaster is actually reasonably designed, whereas the Tormentor Helm...is not.
The standard sidearm of the Dark Eldar and often employed as an off-hand weapon for many warriors who wield two weapons, this pocket-sized weapon does not rate under its larger cousins in any way in the area of sheer lethality. The Splinter Pistol uses the same ammunition and firing mechanisms as the rifle, although compacted and therefore have shorter range, and with a smaller ammunition crystal to reduce the weight even further.
The Splinter Pistol is the ranged weapon of choice for most the remainder of the Dark Eldar forces, finding frequent use in the ranks of Archons, Wyches, Reaver Jetbikers and most Sybarites and Dracons. Usually paired with a Monomolecular Knife or Claw and used as a pair for added effectiveness in assaults.
The most commonly used weapon in the Dark Eldar Armory, the Splinter Rifle is used by nearly every citizen of Commorragh at some point in their lives, let alone by the Kabalite Warriors (Although, seeing how every citizen in Commorragh is a Kabalite Warrior in all but name, this point may be moot), it is light and accurate enough to fire on the move while still threatening the enemy with a hail of lethally poisoned splinters.
The weapon is lightweight and usually sports Monomolecular Blades for added functionality in melee combat. It features a medium sized ammunition crystal to reduce weight while still maintaining a decent amount of ammo before the user needs to reload.
The gun houses an ammunition disintegration generator to break up the crystal into shards, along with a cyclic ammunition feeder to house the shards before firing. Once fired, it routes the energy used to disintegrate the ammunition crystal through a magno-electric impulse chamber that accelerates the crystal to supersonic speeds, rocketing it towards its intended target.
Larger than a Splinter Rifle but not by much, the Shardcarbine fires more reliable and faster than its smaller version at the cost of some maximum range. Favored by many experienced warriors, Scourges and other who thrive on causing pain and death. (Wait isn’t that all Dark Eldar)
The Shardcarbine has an enlarged barrel able to launch even greater volleys of toxic crystal-ammunition than the normal Splinter Rifle without interrupting the shooter at all. This weapon's range is little bit shorter than a splinter rifle and is favored by Scourges. Some Trueborns prefer this gun over others they would be able to possess.
The biggest version of the weapons, the Splinter Cannon is small enough to be carried by an infantryman and can still release a lethal hail of fire capable of wiping out entire swathes of infantry at the same time.
The primary additions are a semi-liquid stabilization mechanism housed approximately in the center of the cannon, to provide a counterweight to the constantly fluctuating center of gravity on the weapon. Second, an auto-burst trigger will continue to fire splinters for four to five seconds after it has been pulled, in case the user loses his grip temporarily during the charge. Finally, and possibly most important, is the addition of magneto-impulse directional spines along the barrel, and a secondary power generator housed in the back of the cannon, to prevent stalling or improper functioning. These directional spines provide additional magnetic field stability, preventing the splinters from exiting the barrel traveling at an awkward angle or hitting the inside of the barrel and causing damage to the weapon.
This weapon has two modes of fire: the regular that allows for the user to move and shoot at the same time, or the heavy mode that delivers a higher rate of fire but requires the wearer to brace due to the weapon's increased recoil.
The Dark Eldar's Goblin Glider rippoffs would have their own take of its weaponry too.
Somewhere between the Splinter Rifle and the Shardcarbine, the Splinter Pods mounted under the Skyboards of the Hellions are designed to fire without a conventional trigger and can still deliver a considerable amount of firepower while on the move. As it is mounted on the Skyboard, the Splinter Pods always come in two, thus they are always twin-linked for twice the fun and pain.
These pods can be fired with the depression of a heel-stud, making them easy to use even assaulting against an enemy squad.