An answer to your question from unreal engine forums
Here is the top answer from there in case the link dies. I did not write this code I simply found it with a quick google of your problem which you stated you already tried.
Link answer:
Get the "velocity" of the target player. Multiply by the time the bullet will take to travel to the target. Then get the position of the target, add the velocity*time vector, and that's the position you should aim at. You can either hard-code the travel time (half a second, or whatever,) or you can in turn measure the distance between AI and player, and divide by bullet travel time, to come up with an approximate travel time. You can also apply a differential equation to calculate the exact time of impact and exact direction, but that requires a little more math and is slightly harder to write out, so I think the above will work best for you.
Simply:
Distance = Length(Target_Position - Firing_Position)
Time = Distance / Bullet_Speed
Predicted_Position = Target_Position + (Target_Velocity * Time)