A milliradian or a mil-dot is a form of measurement used in scopes to help determine the distance between you and your target. I've also included a few tips on what range to zero your M4 rifle at.
Zeroing Your M4
You should zero your M4 rifle for 50 yards. Why?
What you are doing is setting up your line of sight to trajectory. This basically means that you are aiming at the target with the direction and flow of the bullet in mind.
To specify, if you zero your M4 for 50 yards, that means that at 5 - 25 yards your shot is going to be 6 inches below where you are aiming. In other words, if you aim for the middle of the forehead, you're going to hit the nose or the mouth.
Now, obviously the closer you get to 50 yards, the more your likely your bullet will be to hit where you are aiming at. Then, once you get to 50 it becomes point of aim = point of impact.
What happens Further Out?
Additionally, at 100 yards, you are 1 inch high. For example, if you aim for the nose, you'll hit right in between the eyes. This means that you can do a precision head shot at 50, 100, 25 and even 5 yards if you need to. This is because you now know what the hold-overs are. (Where to compensate your aim according to how far away the target is.)
Furthermore, at 150 yards, you are exactly 3 - 4 inches high. This means that if you were to aim for the mouth/chin, you would hit in between right in between the eyes. Once again, you're doing a head shot at 150 yards with your M4!
200 Yards and Further
After your bullet passes 150 yards, it starts to drop. This means that at 200 yards, your bullet will be point of aim = point of impact (if your M4 was zeroed at 50 yards.) To sum it up, at 50 yards and 200 yards, where you aim is where you are going to hit.
That being said, at 200 yards, depending upon your grouping, you could pull off a head shot. This especially applies if you have a longer barrel (say, 20 inches.)
Now passed 250 yards, if you aim for the shoulders, you're going to hit dead center of the chest. So if your target has armor on, you can aim right for the chest. As a result, you'll hit them right in the groin (passed the armor and still potentially fatal.)
300 Yards Out
Once you get to 300 yards, you'll need to aim for right in between the eyes to hit the target in the chest.
Lastly, if you try to hit a target much further than 300 yards, it is not going to do you much good. Because with a standard M4, the bullets will start going sideways. Not to mention that your grouping has now gotten so large that your chances of wounding your target instead of killing them is much higher (if you can hit them at all.)
In conclusion, I wanted to sum up why you should zero your M4 for 50 yards. Because you can pretty well cover any distance from 200 yards inwards with ease. That is of course, if you can remember where to aim from what distance.
To recap, you'll aim a little low at 5 - 25 yards. At 50 yards, you'll be dead on. At 100 you'll need to aim just a tiny bit higher (which really isn't enough to matter.)
Furthermore your average firefight (especially with a rifle) is no longer than 70 yards apart.
The Milliradian Scale or Mil-Dots
Now to be frank, mil-dots are much easier explained in the video than writing it all down in an article. As a result, I'm really going to encourage you to watch that. I start talking about mil-dots in specific at 5:06.
(The book that I'm using in the video to explain mil-dots is called a dope (or data) book that I purchased from storm tactical.)
Also, this article right here goes into further detail if you would like to learn more.
Thoughts?
I hope this article and video helped you out. If you liked it, or if you have anything that you would like to add, please let me know in the comments below.
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