I'd suggest increasing orc spawn rate at later levels or lowering the amount of orcs you need to kill for the orc hunter achievement to at most 100 but preferably less. I've killed enough minors to complete their hunter experiment twice, enough trappers for 3 and enough marksmen for almost 5. But I'm only at 85 orcs so far with the goal being 150.
I can appreciate that some experiments will be harder then others but this one is just overly grindy. It would probably take me 1.5-2 hours of grinding with infinite ammo to get the rest of them if not more.
EDIT: Abby could use the same treatment. By the time I finished the other 3 hunter experiments for FER I was only on 40-something Abby kills out of 200.