Ooff, i picked "Viper", because i think its link to something real and common can let people easily associate it with a trait; "its bite is dangerous".
On the other hand, that could lead to the problem that the real counterpart character will be forced upon the weapon, making changes necessary that would affect its functioning; "its bite is venomous". (but i think that could prove interesting)
Regarding names starting with X i don't feel comfortable with any suggestions that have been posted. "Xonic", "Xonar".... "Xion"? (my favs) - it all is awkward.
BUT why should THAT gun be representative for Xonotic, anyway?
Then there could be a common naming pattern used for all weapons:
XPress
XTazer
XTelzior
XCaliber (LOLWTF?!)
(It's funny, because "XCaliber" sounds like "
Excalibur")
4m038105 - Be the change.