Either you missed almost every shot or something was off with your connection... cause if you're standing point blank range and shooting that weapon, I'm assuming you were shooting someone in the back, that guy shouldn't even have the time to react if he has anything less than blue shield. Blue shield = he can still jump but if you're aim's on him, he'll not even make it to the peak of the jump. Purple/gold armor = he can turn around and actually get some shots off...
I even made a clip of how I approached a gibraltar who was inside a house. Opened the door and the gibraltar was facing my direction. I got the first shot in him and basically all he could do was attempt a jump, but before he was even midway he was already dead.