Master of SecondariesG 15

Getting mastery on secondary weapons is simple, just a grind - 150 kills per weapon, so 900 kills total across the 6 weapons. Get yourself in big, nasty firefights, get it gradually over time, blast the same couple guys and keep reloading a save, it’s up to you. No real trick to it (aside from turning down the difficulty so you can be more reckless) you just need to get kills.