Has anyone else gotten this achievement:

There's actually a very easy way to complete this achievement:
Requirements2 controllers OR another player (slave player)
Map: Rocky Cove
Mode: Team Territories
Type: Custom with Infinite Respawn, Helos, Central Base Territory, Occupy, Time
Time: 60 Minutes
Leave the rest as it is
Method1. Have the Slave player (or second player) occupy the central territory. This will spawn a Helo from the Castle on the far right of the map
2. Now you have to shoot it down. You can do this using several weapons including the Rockets, the M60, and even the Sniper. I personally used the SR S50 Sniper which takes the Helo down in 4 shots. Where you need to be to shoot the Helo is up to you, but I found it easy to stand somewhere between the lake and the ocean
3. Once you have shot the Helo down, move the Slave player off the territory and on again. This will spawn another Helo from the Castle again. Rinse and repeat

Note: Do not move the Slave Player off the Territory until the Helo is completely destroyed. If you move the slave player off the territory while the Helo is still alive, it will just explode and not count towards a kill
First I tried doing 30 minutes and I was able to shoot down exactly 50 Helos. Then I tried 15 minutes and was able to shoot down 25 Helos so in 60 Minutes you should be able to shoot down 100 Helos

But perhaps its best to familiarise yourself with the method before going for a long run. Remember you'll get the 'Achievement Unlocked' notification in-game once you have shot down the 100th Helo
Have fun

Mobius, that is not the fastest way to get the 100 helicopters achievement. The fastest is playin Solo Territory at the map Desert Gulch. By setting the time limit to 10 minutes i am able to shoot down 40 helicopters.