From Lexicanum

A conversion beam projector, often called a "conversion beamer" or simply a "beamer", is a form of heavy weapon.

The conversion beamer fires a high intensity energy beam, which transforms matter into pure energy. A heavily armoured target or dense material will be rent apart as its matter explodes. The more dense the material of the target, the more energy that is converted, making conversion beamers particularly good against heavily armoured troops, vehicles and buildings (smaller versions are often carried by Terminator Marines for cutting through bulkheads when exploring Space Hulks). The intensity of the beam increases as it extends further from the weapon, becoming increasingly dangerous, until it reaches the focal point where the beam is so intense that the energy has to be released in a violent explosion.

An unfortunate downside to conversion beamers is that they are incredibly large and heavy (as they require a number of massive capacitors that line the projection tube) and must remain absolutely motionless when operated, or the intensity of the beam will be negated, rendering the shot useless. Because of this, conversion beamers are usually fitted to self-propelled, wheeled carriages or anti-gravity platforms (the operators will often remain at a safe distance using some form of remote control). Users of the somewhat smaller hand-held versions are forced to wear boots with special claws to provide more stable purchase.

Another problem with the conversion beamer is the length of time they need build up the energy that is released in the beam. Although it is only a second or so, it is easily long enough for potential targets to have moved or escape the field of fire.

In the third edition of the rule book, the conversion beamer was removed, as was the case with the many kinds of missile seen in the second edition rule book.

However, it is once again useable with the Space marine Master of the forge, though it replaces all other wargear.

Sources

• Warhammer 40,000: Wargear (second edition)
• Codex: Space Marines (5th Edition)