Unlike traditional laser-based weapons; the beamer fires an energy beam that converts that matter of its target into pure, explosive energy. Thus, high-density targets like tanks or power-armored infantry would be instantly vaporized in a violent explosion upon contact with a conversion beam.
While powerful, its downside is that Conversion Beamers are incredibly heavy weapons, more so than the likes of the lascannon or heavy bolter, and the user must remain completely still for the beam to be effective while firing (not an easy feat in a universe where close combat is the norm). Additionally, now that AIs are illegal all the myriad preparatory and in-firing calculations necessary to keep the weapon from vaporising everything within a six mile radius have to be done by its user, which generally limits its use only to Techpriests, their Space Marine counterparts, and unusually ballsy Inquisitors with about thirty servo-skulls doing the heavy processing.
Basically an upscaled Conversion Beamer. An Eradication Beamer is a specialized weapon utilized exclusively by the warriors of the Skitarii Legion of the Adeptus Mechanicus. Only found mounted on Onager Dunecrawlers, when fired, the thin yellow beam of an Eradication Beamer widens as it projects outwards from the weapon's distinctive muzzle.
Those in further out from the weapon will be ravaged on a molecular level by its impossible technologies, whilst those closer by are simply atomized, their physical forms scattered to the hot winds of war without a sound.
The Eradication Beamer works in the same way as its smaller cousin does. In 8th edition, it is now a Heavy D6 Str8 AP-2 D1d3 gun that allows one to comfortably tackle MEQs and even TEQs like assault terminators from 13"-36", whilst still maintaining its role as a dedicated anti-tank weapon. This is its main range mind you, which makes this a very versatile weapon. At 12" and closer it gains AP-4 and D1d6, but halves its shots to D3, although it is a gamble since the Onager is not known to be a CQC power house.
Heavy Conversion Beamer
The Heavy Conversion Beamer is a vehicle weapons system used by both the Imperium of Man and the Chaos Space Marines and it is the big brother of the Conversion Beamer. Heavy Conversion Beamers are an ancient relic-weapon of incredible and poorly-understood power. They are very rare and deadly antimatter-based pre-Heresy archeotech weapons most likely developed during the Dark Age of Technology. The Heavy Conversion Beamer is a larger, vehicle-mounted variant of the man-portable Conversion Beamer.
Conversion Beamers are esoteric weapons that are both difficult to construct and highly complex to use, needing skilled calibration to operate as well as dedicated reactor core systems to power, especially the larger variants. As a result of this complexity, Conversion Beamers were primarily used during the Great Crusade and Horus Heresy eras in the late 30th and early 31st Millennia for dedicated siege warfare and anti-armor operations.
In the late 41st Millennium, Conversion Beamers and Heavy Conversion Beamers are incredibly rare pre-Heresy technological artifacts, and their conservation and deployment is typically the responsibility of a Space Marine Chapter's Master of the Forge. The Heavy Conversion Beamer is even rarer in the late 41st Millennium than its smaller counterpart, as it was mostly equipped on the Contemptor Pattern Dreadnought and Deimos Predator Executioner vehicles.
Conversion Beam Cannon
The big daddy of the Conversion Beamers that is mounted fittingly, on the big cheese of Imperial Knights, the Acastus Knight Asterius. The Conversion Beam Cannon looks like a twin-linked Heavy Conversion Beamer that some Techpriest decided to simply ducktape it and said, "Fuck it! We need an Acastus Knight that could deal with hordes of infantry and tanks!"
Due to the cost and difficulties in making a Conversion Beam Cannon, let alone in factoring the cost and expense in making a new Acastus Knight design, these weapons were pretty darned rare by the turn of the Horus Heresy. It wouldn't be surprising that by the turn of the 42nd Millennium, only a few of these bad boys are left, locked up in the vaults of Mars.
On tabletop, these things are one of the ultimate vehicle tarpit killers. Oh yes, this thing deals with vehicle hordes. With a range of 42-72", this monster of a Conversion Beamer is not only a Ordnance 1 weapon, but it is also a S10, AP1 weapon with a 7" Massive Blast template. It also has Sunder which re-rolls failed AP rolls and Wrecker that deals a +1 damage on fortifications. Oh yeah, did we forget to mention that the Asterius carries two of them!? Anal circumference indeed.