It is hard to kill someone with helicopter miniguns most of the time. I managed to kill like 5 people only when helicopter was hovering completely still in the air, but in a moment we took a hit with RPG.
Both crosshair and camera are shaking very much and it's hard to precisely aim at the targets, even at static targets like campers.
My suggestion how to improve it:
Look at BF4. Helicopter miniguns are much more comfortable to use. The aiming is balanced: crosshair is completely still, but the camera is shaking while shooting. So, improve aim first. ||I remember cars' machineguns had static crosshair, but it was changed to dynamic. Personally I preferred static one.||
BBR should have helicopter miniguns that are comfortable to use and aim with, and then you can balance damage if it will become OP, but please, make them at least as good as in BF4.
Examples of shooting from current miniguns (bad fps, it was actually a bit better, but you got the idea):