Lag should not effect gunnery directly.
HT or skuzzy can probably explain this better than I can.
However, you see the plane, you shoot, your front end sends a packet to tell the other plane if you hit & where & how often.
If this packet is delayed, you can get a delay from when you shot, to when you see him die. We've all seen people come at us shooting, only to have a wing fall off behind us, or have our wing fall off after he's zooming up for the next pass.
If your consistantly loseing packets you should also be loseing connection, switching to TCP/ip instead of UDP.
The easy way to test if its connection related is same plane, same guns, shoot a plane & destroy it.
Then shoot a ground object & destroy it. If your loseing packets thats where it would show up.