On the Fly Achievement

So I have been playing ALOT of Bioshock: Infinite...I have 3 achievements left and I am currently working on "On the Fly" before tackling 1999 mode. I am having an issue with this one though. I have on the sky-rails moving around and shooting enemies (unarmored mind you) and the kills are not counting. Is there something else I have to do or is it a glitched achievement? I've looked up videos and they aren't showing me anything different. If anyone can help I would really appreciate it. 

^bump

nevermind I got it to work...it was just glitched

Nice. I've only got like 2 achievements left. One of the them is the "kill a handyman by only shooting his heart" one. I don't know how I'm going to pull that off. Those guys go so fast, even if I focus on hitting the heart, it seems damn near impossible to not have any stray shots hit him somewhere else. 

I did get the "Scavenger Hunt" achievement, for beating 1999 mode without using a Dollar Bill machine. That was tense.

http://www.youtube.com/watch?v=-DnM9b-xRKc

easiest thing to get the heartbreaker achievement