The Huntsman 5000 is a powerful rifle, or 'self-reliant multi-purpose weapons system with internally repleneshing ammunition', which adapts to whatever it's fired at to most effectively kill its target.
Other than the tools that Weapons Crests provide, it seems that this is one of the very few weapons that can injure the wielders of Weapons Crests as if they were normal people. Although rarely used, Nikolai rarely goes anywhere without it.
Konstantin Romanov - When Konstantin is holding Jena Makarov by the throat, he states that his "only regret is that Dante is not there to watch [her] squirm." After this, Nikolai shoots the wrist of the hand that is holding her and tells Konstantin to "be careful what [he] wish[es] for." When Konstantin goes to attack him, Nikolai then shoots the wrist of his other hand, And one ankle. Considering Konstantin later heals in a matter of seconds from being cut by Jena's sword from his left shoulder to his right hip, the rifle must be a unique weapon.