This perk consistently bugs out and doesn't work. While doing "Sword of Crota, " it was activating when I killed Hive with my fusion rifle that has the perk, but then on the next level I did (also solo), "The Stranger's Call," the ability was not activating when I got one shot kills on the Vex you encounter in the library area. I even switched to my Matador 64, which also has Army of One in the last perk slot to test if it was just my Snakebite Surgeon bugging out, but even with the ridiculously OP, 12-foot range, one-shotting shotgun, the perk was not activating.