I will be building 4 ARs in the next 6 months. Ive done some searching but Im just digging myself deeper.

#1 will be an M4gery 14.5" barrel Flattop with RAS as my go to gun. Needs to be reliable and acurate to 200 yards and must be able to function after being submerged in water. I would like all batteries to be the same.

  What optics? Im torn between the Aimpoint Comp ML2 and the EOTech 512
  What BUIS? I havent a clue here
  What light? Thinking about just a Streamlight M3

I want this done right the first time so Im willing to pay for what works and will stand up to heavy use. What would you suggest and why.

#2 will be in a caliber larger than 5.56 preferably about .30. This will be a scoped, free floated long distance rifle.

  What Caliber that can use USGI 5.56 mags?
  What Optic whould you mount?

#3 & 4 Will be plan 16" 5.56 rifles for my kids. These I have figured out.

#1
Optic - EOtech.  1x magnification, with a big ring for CQB and a inty 1 moa dot in the middle for precision
BUIS - ARMS 40.  It's all you need out to 200 yards
Light - Surefire integrated with vertical grip.  It's all there in one unit so no Macgeyvering needed.

#2
I hear that the 6.8 will fit the 5.56 mags in a pinch, but of course not reccomended by the manufacturer.  As for optic, go with a crazy "caddy shack" high power scope.

for #1 I would say go with the ML2 as an optic and a troy industries BUIS. And any surefire weapons light , at least 9V will be great. I would reccomend a seperate light and vertical foregrip as you will have more mounting options later on. If you want a vertical foregrip, get the TangoDown one.