On the first map Mining Town is a gas station at 25.23 - 19.31 which is also an Outpost. In front of the gas pumps are two enemies located which are not moving. Around these two enemies are patrolling enemies. Go to the position in the video, line up with the two enemies and wait that a third enemy crosses this line, then shoot.




Now if the bots are not working in your favor or all erratic I suggest fast traveling to another map to let that outpost refresh.

and for what sniper to use, this all depends on you. Myself i actually used the starting sniper with armor piercing rounds,