*Just so you know, this is a great achievement to grind for because you can simultaneously complete the camper achievement!
Similar to what XBL iGoldenGirl however, my method is slightly different.
You'll be playing Terrorist Hunt Defense Mission(Protect Hostage) on either
The Consulate or
and you want to choose to defend either
The Consul Office or
The Cigar Lounge
To make it so you only get these maps as well as the game type when you search for a Terrorist Hunt match, go to options>Matchmaking Preferences. From here you can turn off and turn on what you want to search for. Keep in mind that sometimes you won't always get the preferred map however, this does not happen too often.
To start off,
you want to have a shotgun, because there is a 99% chance of it being a one hit kill through any surface at close range.
On both maps, there are a set of two windows that enemies love to rappel into. Rappelling is slow when the AI does it, so this makes them an easy target. You'll be camping these windows for the entire game while your team defends the hostage from the rest of the entrances. The thing is, the windows on these specific maps are normally very active which makes camping these windows a good idea for both pen kills as well as successfully completing all the waves.
Simply barricade the windows, crouch, then punch the bottom area so you can see if the AI is trying to rope up(You'll see a rope). When you see them come up, un-crouch and guesstimate where they are and BAM with your shotgun through the barricade. You can shoot through the broken pieces of the barricade before it completely breaks, too. If you are going to replace the barricade, make sure you don't miss one coming from the other window!The windows on The Consulate are the two windows in the Consul office that are directly next to each other in the back corner!
The windows on The Kafe are the two behind the piano in the Cigar Lounge!
The amount of enemies may vary greatly, but I have gotten a lot of pen kills on cigar lounge in one run! My highest on Cigar Lounge was 14 pen kills! and on the Consul Office it was only a mere 12...
Please note that I played these missions a lot! so a realistic guesstimate of how many you can get is anywhere between 5-9 on average, which is still a lot considering the fact that you'd still be grinding for the camper achievement...ugh.*When playing online, make sure to be either Rook(to give armor to your teammates to ensure their survival) or Doc(obvious reasons).
Thanks guys! this was my first guide so don't be too harsh