The biorifles typically fired yellow bolts of energy. (ENT: "Rajiin", et al.) A direct hit from a biorifle itself was survivable by a Human, at least temporarily. (ENT: "Twilight") A biorifle could also be connected to a Xindi-Reptilian grenade launcher. (ENT: "Rajiin")
The biorifle's power cell was a pair of techno-larvae. Their neural pathways modulated the rifle's power output; Doctor Phlox considered this system the most sophisticated example of biomechanical engineering he had ever seen. The top of the rifle could be easily lifted up, exposing the larvae. If either of the two organisms was removed from the weapon, a new one grew almost immediately to replace it, which made disarming such a weapon very difficult. The organisms could be killed with a sustained burst of delta radiation. Omicron radiation, however, caused the organisms to thrive.
The biorifles worked on a rotating modulation that self-destructed when accessed by other species. A countdown began before detonation, which emitted audible ticks and was displayed on a triangular readout at the top of the weapon, directly behind (from the user's perspective) the compartment which housed the twinned organisms. The countdown was accompanied by a steady increase in the biorifle's energy levels, to the point where the weapon overloaded. (ENT: "The Shipment")
Biorifles were used by Xindi-Reptilians when, in 2153, they invaded the NX-class starship Enterprise and battled with officers aboard the vessel. Since the battle resulted in a Xindi-Reptilian being left on the starship, a biorifle was also left on board. The weapon's range, power output and how the Starfleet crew could defend against it were topics of interest to Captain Jonathan Archer, who hence gave orders for the rifle to be disassembled and studied. (ENT: "Rajiin") Commander Tucker conducted multiple scans of the weapon, discovering it contained organic components, which led him to involve Phlox in the examination. Once the doctor determined that delta radiation could kill the eel-like lifeforms, Tucker theorized Reptilian weapons could be very quickly rendered harmless, if the Starfleet officers rigged up portable EM emitters. Phlox argued that the amount of radiation required would be extremely dangerous to any Humans in the area, but Tucker continued to regard his hypothesis as a viable starting point for a workable defensive strategy. Having learnt all they could from examining the workings of the biorifle, Tucker and Phlox proceeded – somewhat criticized by T'Pol (due largely to the weapon's untested nature) – to test the device by attempting to fire it at a target on board. The weapon didn't allow Tucker to use it and instead began a countdown to self-destruction, so he speedily beamed it off the ship before it detonated. (ENT: "The Shipment")
In an alternate timeline wherein Jonathan Archer was infected with memory-degrading interspatial parasites, biorifles were used by teams of Xindi-Reptilian intruders aboard Enterprise as they forcibly made their way onto the ship, for instance following several months in which the vessel had unsuccessfully searched for the Xindi weapon while under T'Pol's command. Though two Reptilians dropped their own rifles when they were consecutively shot to the ground by MACOs, another Reptilian used his rifle to shoot down a security officer guarding Archer's quarters. The same Reptilian subsequently used the weapon to destroy a panel outside Archer's quarters, thereby accessing the otherwise locked room. However, an ensuing battle between Archer and the Reptilian trespasser caused the latter combatant to drop his rifle. He was about to pick it up again when Archer attacked and killed him.
Rifles were also used by Xindi-Reptilians who violently boarded Enterprise in 2165 of the same timeline. One shot struck a console on the upper level of engineering and caused an explosion which threw Phlox, who had been standing near the console, over the railing to the lower level, where he then lay motionless and unresponsive to Archer checking him. More direct strikes from the Reptilians' rifles gravely wounded T'Pol and Archer before the ship exploded and the timeline was subsequently reset. (ENT: "Twilight")
This form of rifle was designed by junior illustrator Berndt Heidemann. ("Countdown" text commentary, ENT Season 3 DVD) He stated of the weapon, "They [the producers] said it's gotta be something alien – we don't want your typical handle/clip/trigger. And they wanted a rifle with something organic with it – they wanted to add that part of the Xindi, as if they utilized some organics in their technology. It has the flip-top, the whole front comes off, the front slides forward – this was definitely more than your usual gun. And Brannon [Braga] really liked H.R. Giger's art, and he wanted some Giger-esque things on it." (Star Trek: Communicator issue 149, p. 54)