She was fast enough for a pistol. But she couldn't stop an armour piercing round.
–Professor Kakuzawa, just after using the FAMAS to execute Number 3
The Fusil d'Assaut de la Manufacture d'Armes de Saint-Étienne (or Assault Rifle made by Saint-Etienne, an arms manufacturer) model G2 is an assault rifle favored by the French military. It fires high-velocity rounds, that, in the world of Elfen Lied, can kill a Diclonius who is not aware of being targeted. It can be used either as a stationary position weapon or be handled portably. It was used in the anime on at least one memorable if tragic occasion by Professor Kakuzawa.
In the series
As SilpelitNumber 3 made her ill-fated and ultimately pivotal escape attempt, she paused in her revenge-minded slaughter to talk to Kurama, the only staff member to try and stop the experiments that hurt, tortured and killed these girls. Whether she meant to kill Kurama, infect him with the Diclonius Virus (which she did) or truly wished to thank him, the results were all the same. While Number 3 was distracted by Kurama, Professor Kakuzawa grabbed a FAMAS G2 (possibly his own property, or possibly from a fallen guard) aimed at and killed Number 3 by blowing off the back of her head. He was especially gleeful about this kill, an indicator of both his own coldness and the disconnect the Kakuzawas felt towards certain Diclonius, since they believed themselves to be racially connected to the new species.
In the manga, during a training exercise disdained by the blood-thirsty Bando, he discards what appears to be an earlier model FAMAS F1.