Tactical Question - Shooting from a moving platform

Every so often I will be re-posting one of the "Questions of the week" that I have previously posted on the page https://www.facebook.com/groups/AirSplatArmyPuyallup/. Whether you shoot airsoft guns or real steel, there are situations and the laws of physics AND gravity that apply to both. This gives you chance to test your knowledge and perhaps learn new skills.

When shooting from a moving platform such as a helicopter or vehicle at a stationary target that is 30 meters away, moving parallel to the target, on a windless day, you should:

1) Shoot directly at the target
2) Shoot above the target
3) Shoot to the leading / closing side of the target
4) Shoot to the following / trailing side of the target
5) None of the above

Now for the answer: 

As the bullet will have similar lateral movement as the shooter, therefore will be traveling away from the gun as well as "forward" you must shoot to leading / closing edge of the target. Depending on the shooters speed of travel, you have to factor for forward momentum in your shot so that can range from a few inches to a several yards.   

For those that love math a little toooo much:

Let's assume that the shooter is shooting out the door at exactly right angles to the direction of motion.

Then the velocity of the bullet can be found by: 
Square root ( Hv x Hv + Bv x Bv)

 Where Hv is the velocity of the helicopter  and Bv is the muzzle velocity of the bullet. 

Now to get complicated. 

The bullet won't be going at a right angle to the helicopter, it's going to be going at an angle that is a combination of the two directions of travel.

 If the helicopter's speed and the bullet's muzzle velocity were exactly the same speed then the bullet would travel at a 45 degree angle (angled in the direction of the travel of the helicopter).

 But that's not likely.

 The direction of bullet travel can be calculated by:
 Arctangent of (Hv/Bv)

That will give the angle that the bullet will travel (angled from the original right angle path of the bullet toward the direction of travel of the helicopter).

Example: 
Muzzle velocity - 1,000fps
Helicopter speed - 150mph = 220fps
Bullet velocity - 1023.9fps
Bullet angle - 12.4 degrees angled toward the direction of travel of the Helicopter

Padre' out...