Taking Down Helicopters

With the M72 Law, when I look lock onto an attack helicopter and fire, the helicopter makes an evasive maneuver and I miss.

It seems like the best way to take down a helicopter is just to line it up without the scope and fire, is that the best way. I've had some success with this. Are there any other tips for taking down a chopper?

There really isn't a good way to hit a helicopter with the M72 Law, the first rocket is always going to miss. No matter who fired it, either because the helicopter moved or it shot out flares. Your best bet to taking out a helicopter with the M72 is being the second person to fire at the helicopter. Or you could always just equip the Strela-3 which has two rockets rather than just the one.

What I've found is that on the first shot towards it, countermeasures will be launched from a chopper.

Take another shot or die & respawn, your second missile will hit bang on target.