Kellerun assault rifle

From Memory Alpha, the free Star Trek reference.

The Kellerun assault rifle was a weapon employed by the Kellerun military. It fired rapid bursts of green plasma-like energy balls. They were used by the Kellerun assault team that boarded the T'Lani munitions cruiser where Nydrom, Julian Bashir, Miles O'Brien and other scientists were working to dispose of the Harvester biogenic weapon. After fending off the attack, Bashir and O'Brien each took a rifle with them to the surface of T'Lani III where they hid out and waited for Starfleet to come looking for them. (DS9: "Armageddon Game")

Kellerun assault rifle taken from a soldier Bashir had just beaten into unconsciousness

Kellerun assault rifle being used to destroy some dangerous knowledge

A shot from a Kellerun assault rifle hits Nydrom

This prop began as the Hunter's weapon from "Captive Pursuit" and later became the Jem'Hadar plasma rifle used is several episodes.