Plasma rifles or plasma casters are high-tech weapons which find numerous applications in military and industrial fields. They fire superheated bolts of plasma powered by either microfusion cells or heavy energy cells. The bolt forms in a special chamber, which is then sent down a superconducting barrel, propelled by, and in some models stabilized by electromagnetic claws upon exiting it.
Initially, the weapon was a bulky, industrial plasma caster, manufactured by Winchester Arms; while it performed admirably, it was expensive and required specialized training to use. However, later developments for the US Army would lead to a more compact design that was cheaper to produce and easier to train for, perfectly suited for urban warfare.
Regardless, all types of plasma weapons have a common feature: when a critical hit is delivered, they can literally melt down enemies. While most industrial casters aren't powerful enough to dissolve bones too, subsequent models have no problem converting the target into a puddle of goo.
The plasma caster is a powerful energy weapon, having a rather low AP cost and high rate of fire. Its precision in V.A.T.S. suffers if a character cannot meet the steep Energy Weapons skill requirement (100) and at 20 pounds it was the heaviest energy weapon in the game prior to the advent of the GRA Cleansing Flame. It's rare and not very durable, so the Jury Rigging perk or weapon repair kits may be necessary for continuous use of this weapon.
When viewed in third-person, depending on what armor you're wearing, the plasma caster may not be visible on the player character when holstered. Half-way through the holstering animation, the weapon model simply disappears, similar to the incinerator and heavy incinerator. If visible, the player character holds it in one hand with the pronged tip clipping through the ground.
In the G.E.C.K. there is a plasma caster critical effect explosion that was cut out from the game. In the projectiles window, the explosion is already set but is unchecked.
Without any DLCs, there is only one fixed plasma caster in Fallout: New Vegas.
The naming of this weapon "Plasma Caster" instead of "Plasma Rifle" like in the original games was both because Fallout 3 had already introduced a plasma rifle, and that the weapon does not look like a rifle 
pcps3xbox360 The weapon fails to fire a projectile properly when used in third-person view. After equipping it when in third-person view it may not work even when switching to first-person view. Re-equipping it while in first-person view may solve this. [verified]
pc Sometimes after quick loading the weapon is held in one hand by the handle and moves with the players arm movement when holstered, or appears next to the players arm. This can be fixed by un-equipping and then re-equipping the plasma caster. [verified]
xbox360 When using the weapon in V.A.T.S. the projectile will often not fire unless very close to the target, and if standing under a roof the projectile may collide with the structure. [verified]
xbox360 While equipped, weapon may become stuck to player's hand when changing outfits. To fix this, simply un-equip, then re-equip. [verified]