Had some troubles getting the Vanguard specialization to unlock. As it turned out, it required me to get kills with specifically machine pistols at 7 blocks or less. The description for how to unlock it says to get kills with ranged weapons at 7 blocks or less. This is fairly misleading and I only came to the idea of using machine pistols when I looked at the specialization's description.

The suggestion is clarifying on the wording to say that you need to get kills with machine pistols specifically within 7 blocks or less to unlock it. That or making it count kills with any ranged weapons count as long as the kills are within 7 blocks or less of you.