Re: Aerial Sniping Info
Your M-107 will be money off a loosely hung strop across the door, the gun hanging in your strop will greatly reduce vibration, of course some helos vibrate more than others. A piece of 1" webbing with an adjustable buckle and a clip/caribiner on each end will give you versitility, and the ability to quickly adjust strop length for different altitudes/shooting positions and can be adjusted in seconds. This works well with the weight of the Barrett.
S&B 1x4 SD is a common piece of gear, the newer 1-8 would be great, as are eotech/aimpoint/acog type sights. Low power optic of choice, whatever you prefer. Your Mark 4s dialed down will still be a bit high on mag.
Lots of the old training material on aerial gunnery is just that, old and more geared toward machine guns, door gunners and supressive fire than precision rifle fire. Forward throw, and rotor wash won't make much difference in real world scenarios/ranges, I say this because you will likely shorten the distance some, 400m is a hell of a shot from a helo . You can work techniques for both hover fire and running fire to handle different scenarios and ranges.
I will say this, 150yds with you and target traveling at 50mph in step will make for challenging shooting. Much easier if collateral damage is not a concern . Add in the fact that the target vehicle will likely be traveling on less than perfectly flat road, and will be maneuvering agressively/evasively, then figure in the pilots, the wind...ect ect .
Personal preference will also dictate position. Some guys take a knee, some sit , some prone out, it will take practice to see what works for you and what your aricraft config will allow. Also how constrained by policy you are will also weigh in here. I will say this, if you are developing a SOP try to leave it a bit vague so there is some leeway with your set up.