A Starfleet prototype rifle firing chemically propelled tritanium bullets, designed for environments where phasers fail, which a Vulcan officer fitted with a micro-transporter to commit murders on Deep Space 9.
The TR-116 was developed by Starfleet Security for use in dampening fields and radiogenic environments where energy weapons will not work. It fires a solid tritanium bullet. The design was shelved when regenerative phasers arrived, but the replicator pattern remained on file.
In the Deep Space Nine episode Field of Fire, three Starfleet officers on the station are shot at close range in locked rooms. The killer has attached a micro-transporter to the barrel, which beams the bullet to within centimetres of the victim, and aims through walls with an exographic targeting sensor.
Ezri Dax, drawing on the memories of the murderous former host Joran, builds a copy of the weapon and identifies the killer as the Vulcan science officer Chu'lak, whom she wounds with the rifle.