Before the Reapers supposedly switched to their armour they created a guns of unrivalved power and range. Incredibly powerful and incredibly advancd but limited by their size and recharge times they were soon destroyed save for for a couple hundred kept on display in museums or on certain family vessels that helped make them.
Their power source seems to be the of the same material that power their ships and is wildy more powerful than even white kalminite. The energy from this material is so strong that it disorts space around as if you were looking into a jet stream.
To beings with blood short term uses even in Taiidans can cause signs of radiation poisoning. It doesn't seem to be centered on which races fare better in radiation just any race with blood seems effected by it.
Result when firing the weapon at a target makes the molcules of the target lose size and denisty turning the body into a variety of other substances. Prolonged exposure can turn th eentire body to hydrogen and send it into a nuclear reaction, which can deal massive damage to anything nearby even to the user. That is unless they are armoured with Reaperium armour. Then even a two blackholes smashing together would sooner break than the armour shattering much less vibrateing.