First off, if you think this is a difficult achievement, I have 2 things to say to you. #1, you are correct and #2 if I can do it, you can do it, too. I'm much more used to playing first-person shooters like Doom, Unreal Tournament and Left 4 Dead (mostly old school FPSs) so I've always been a little leery of playing Call of Duty titles, especially the Modern Warfare games.
That being said, I thought I'd never be able to get anywhere in this game, let alone get the Pit Boss achievement. Let me tell you, you will fail many MANY attempts at getting this, but here's how I was able to overcome this achievement on my last attempt after about 50 of 'em.
Let's gear up, shall we? Pick up pistols. Yes, pistols is what will save you here. Use the M9 and the USP .45 for this achievement. Use them in that order. The M9 is VERY accurate and the USP .45 holds a good clip.
The rules of the game are:
1. Do NOT hit civilians. Not even one.
2. Do NOT miss any enemies. Not even one.
3. Run as much as possible, especially on straight paths.
4. Switch weapons from your M9 to your USP .45 instead of reloading your M9. You usually run out of ammo for your M9 about the time when you're on the stairs before you melee the target that "surprises" you before stepping onto the roof. You may run out earlier than that depending on your skill of accuracy, so switch weapons and don't reload.
5. Reload in mid air as you jump off the roof. It's okay to reload here.
6. If possible, take out 2 targets with 1 shot. I've done it 5 times in 1 run through the pit, so there are opportunities. 1 in front of building, inside first floor of building, on top of roof of building, and 2 opportunities on ground after you jump off the roof before the Pit's exit.
The better your accuracy, the more time that's shaved off your time as a bonus. I actually ran the pit over 30 seconds, but unlocked the achievement due to the accuracy bonus shaving off 5 seconds of my final time. That's pretty much how you're going to unlock this achievement as it is near imposible to run through under 30 seconds. I'm pretty sure it is impossible without skipping every target LOL. You do not get time bonuses for not hitting civilians and hitting all enemies, but you do get time ADDED ON for hitting civilians and missing enemies. That is why I told you not to do so in my instructions.
So, how did I fare? Well, here's my stats:
My Time: 33.8 sec
Accuracy: 104% (I don't know either LOL)
Accuracy Bonus: -5 sec
Civilians Killed: 0/11
Enemies Killed: 24/24
Final Time 28.8 sec
Recommended Difficulty: Veteran
Guess I shouldn't worry too much about being good at newer FPSs!
I've included a helpful video from a genius team of gamers called "Achievement Hunter" that works at Rooster Teeth, the makers of the popular Halo machinima "Red Vs. Blue". See it below and "Good luck! You'll need it" ;)