The trick with the 30mm is to force the other plane into a knife fight, then when he is close, (100<) pop one in his general direction. Basically, be close. Also, visualize the shot before it happens and set it up. Plan ahead of time, on how your going to setup the shot. For example, try and bait the guy to drop his nose and dive on you, then pull up and into a reversal, and take the snap shot.
Ardy's got it. Anticipation is the key.
To hit with the tater (keeping in mind that my gunnery is the worst there is), you need a couple criteria to be satisfied:
1.) Accurate anticipation of the EAC's flight path (5-6 seconds ahead). This is usually the easy part as the majority of MA drivers will resort to a flat turn if in trouble.
2.) Roll your AC so that you need only worry about ballistics on a single plain. In other words, you want your wings perpendicular with the EAC's path of flight. This way, you dont have to make adjustments for lateral displacement of the round.
3.) Always shoot with the intention of hitting with the first round. That advice was given to me by moot years back (and from Agent360 to him, IIRC) and it made a heck of a lot of difference. 60 rounds doesn't exactly provide for a lengthy firing time and the space in between each round as it travels through the air is fairly significant. Its significant enough that if you try and "paint" the area where you think the EAC will be, per #1, he and four friends (exaggerating) can fly in between one round and the next without worry. If you have a shot, take it and limit it to 5 rounds, max. If your probability of hitting your target is low, don't pull the trigger - continue the setup until you have the shot you want. The K4's most excellent advantage is the ability to dictate the fight in the vertical which means you don't need to hope for a snapshot. If you have the time (admittedly rare in the MA), you should be able to work the EAC into a position where you can not possibly miss.
And use that throttle... 100% Mil and WEP aren't the only two options. Torque it to the left; chop it to the right. You'll get your shot eventually.