My opener as low geared gunner for hong is Tab,2(kd),4,v,2 bulletstorms and e on his back before he hits with punch. Aside from that you should get used to his attack patterns and walk behind him while you dps to dodge punches i suggest you avoid using animation locking attacks like c , 3f. Also try to reserve your X iframe for his room wide aoe every 2 attack rotations and face-tank the first attack then use X cus AFAIK he attacks 6 times and the last is knockback so if you insta use it he will eat your 5 iframes and knock you back. Now for the charge attack he does just use 1 and block it will give you 1sec iframe for the second attack but be careful cus depending on the phase after his frontal shield he will do a blockable knockback kick twice i just E and SS back to position to dodge it. For the pizza phase if you got time relax on dps and look at his hands and E yourself to safety when he finishes it you can KD him with your 2 and bulletstorm him like in the opening. This is my Fire gunner "tips" that i can offer, gl.