World English Dictionary
sniper (ˈsnaɪpə)
n
a rifleman who fires from a concealed place, esp a military marksman who fires from cover usually at long ranges at individual enemy soldiers
You don't use your sniper. That would be like saying that you use your fast. It is poor english. A sniper is is a person, a job. It is not a rifle. A rifle may be used by a sniper, thus making it a "sniper rifle".