This tells that you need to get 79 GG kills in Golden Gun mode. Unlike iSHOCKWAVE 1993, I would recommend firing while moving rapidly because you have less chance of getting shot from a distance and the crosshair doesn't get bigger as you move. But if you can get a good shot without moving, by all means, take it.
Sometimes(like me) it won't be just 79 kills. After I hit the "magic number", no achievement popped. I kept playing and finally got the pop at 159 kills. I WAS REALLY MAD.
But, like Clobbering and Boys with Toys for me, the achievement might pop really early, so just keep killing until it comes.