The weekly role based Drifter bounties are designed to give you helmets in a series over multiple weeks. Let's say you grab the reaper weekly bounty. The first time you complete it, you will be rewarded with a illicit (+1) helmet. The following week, when you complete the weekly reaper bounty you will be rewarded with a outlawed (+2) helmet. On the third and final week completing the bounty will reward you with a notorious (+3) helmet. All other armor drops are based on your synthesizer and what motes you wager.