Lily armed with a M960
An M960 firing
The Calico M960 was a submachine gun used in the 20th and 21st centuries.
In 2063, Lily Sloane used an M960 to defend the Phoenix silo in Bozeman, Montana when Jean-Luc Picard and Data were in the facility. The weapon had a high rate of fire should it have been needed to stop a humanoid, but was completely ineffective against Data's android body. (Star Trek: First Contact)
The Internet Movie Firearms Database identified this weapon as the Calico M951. It was outfitted with a weaponlight and an EOTech red dot sight.