The last assignment I'm trying to get done is the PKP specialist. I need about 17 more claymore kills to complete it, but I'm having a pretty difficult time. I usually go to a small map with lots of chokepoints like Metro, plant 2 claymores (usually on the escalators). I've noticed that sometimes the claymore will explode and injure the enemy but will not kill them, and other time they can walk right in front of if and continue on their merry way without even setting the claymore off.
Tips, suggestions, etc?