"A stream of charged particles seeks the single nearest hostile target and locks onto them until they are fried. The Proton Arc makes eliminating powerful enemies very easy indeed."
The CM Proton Arc is a Laser, that was mentioned as being added to the game on the April 28, 2016 update, though it was unobtainable without hacks. It was paired with the Zerfallen, as it was discovered in the game's files to be right next to the aforementioned weapon and was added simultaneously.
It has the largest "blast radius" of all explosive weapons in the entire game. In fact, it's one hundred times larger than Luftplatzen (2nd largest). Also, it has the highest Damage per second in the entire game, surpassing even the HIKS M1000, though it is limited by its one pierce which can't be increased, making it almost solely a bossing weapon. The only instance of higher damage per second would be the Zerfallen, but the Zerfallen requires a long reload and quite often so, meaning the damage would only briefly surpass it. Proton Arc works by auto-targeting and damaging the nearest enemy to the player and will only switch target when the original target dies or if the original target becomes out of range. The center of the blast range is the user itself, so Proton arc can even target zombies behind the user.
There is a small delay on switching between targets, however, this doesn't apply to Puke worms as Proton Arc will kill a group of pukeworms almost instantly.
It costs 350 NK coins or $34.99 USD & a character of level 50+ is required. CM Proton Arc appears in the store along with Zerfallen and Torment
Adding piercing is completely useless because even with two pierce the Proton Arc will only target one zombie at a time.
Proton Arc has the largest "blast radius" of all explosive weapons in the entire game.
The Proton Arc will still continue to fire even if you run behind walls/barricades, however, it can't target a zombie behind walls/barricades.