I know these guys are not easy, but I cam up with a way to eliminate them in a way that might or might not hurt you. This trick is all about perfection, but once you learn it, those guys are easy. Once you shoot him once, he flinches, thats hen you strike. Make sure you have some sort of machine gun. After he flinches, run in front of him, but not in his range of bashing, and start at him with a machine gun. He can't shoot you cause hes to busy flinching! Easy way to kill, but hard to learn!
When goin down from you parachute, just act normal and make sure you fly toward where you want to go, but when you go to land, thrust the stick forward to go striat, and land like that. This is a greased landing and you get an achievment from it.