When it comes to properly zeroing in your AR-15 rifle, there are many schools of thought on the proper way to do it. Personally, because of the help and information I received from from Mr. McQuay from M2Tactical, I will always zero my AR-15 rifles for 50 yards. Please allow me to explain why.
In the video linked above, you will discover why a 50 yard zero for the AR-15 style rifle is my favorite way to zero. With my set up, I have a 1:7 twist ratio barrel and for a sight I have an Aimpoint PRO with a 2MOA dot. I had originally zeroed my rifle for 100 yards. When I placed my red dot on the bullseye at 100 yards, assuming I exercised my marksmanship fundamentals well, I would hit it. However, with that zero, when tried to shoot a target at 25 yards, I found my aim was off quite a bit. With self defense in mind, would I want to place the red dot/sights where I want the bullet to go (point of aim = point of impact), and then pull the trigger without thinking about bullet drop and elevation? Definitely. That is why the 50 yard zero is so important for my shooting purposes.
 What is bullet drop?
Remember from school that whatever goes up, must come down? Think of that when thinking of bullet drop. When you pull the trigger on your AR-15, the bullet leaves the barrel traveling very fast, soaring through the air and falling, that is, losing elevation, because of gravity. Point of aim is a straight line from your eye to the target, but the bullet travels slightly above and below that line depending on distance. This is why a 50 yard zero is simple. Take a look at the picture M2Tactical provided me for a better visual on bullet drop, point of aim, and point of impact.
Why zero for 50 yards?
There is one key reason I choose to zero at 50 yards, and that is simplicity. Because of bullet drop, a 50 yard zero allows one to place their point of aim on center of mass from 25 out to 300 yards and the bullet will strike the target. So, in other words, I can place my red dot (or point of aim) on my target from 25 yards all the way out to 300 yards and I will hit my target (again, assuming I exercise good marksmanship fundamentals) with only a spread of roughly six inches from point of aim to point of impact. This allows the shooter to take a lot of guess work out of where to aim. Place the red dot on the target, pull the trigger, and you will hit it.
