If you concentrate enough and be very patient you can get like 20000xp every 20 mins. And then when you run out of ammo reload the checkpoint. But I don't think many people would sit there for 7-8 hours doing something sooo boring.

Me and my friend only did this for 30 mins because it is very boring. What we did is when one person needed to reload the other went and when he needed to reload I went and so on.

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