50 hours should be easily obtainable especially if you can sit idle for some time or just through plain playing the game. Looking at the steam achievements the 100k barrels has been unlocked by 9.1% of players and seeing as the steam community aren't as obsessive over achievements as us 360 players it should also come through playing the game. In fact I would guess by looking at those achievements most will come naturally.
Destiny Raid completed 04/11/14
Destiny hard Raid completed 02/12/14