Hitting a helicopter on Call of Duty is not as easy in real life, man. Especially with a single-shot deer rifle. Good luck.
We were rarely hit with AK fire at lower altitudes... so higher altitudes do help in that regard. The concept of leading a target is hard for many to grasp.
Good call on the 'loud bang" concept below. It's more of a light thunk if it didn't hit anything serious.