Zero Drop: a quick intro to zeroing your AR-15
Hey guys, quick post to explain what a Zero is in the context of firearms, as it’s being argued over on Gun Twitter RN and I made a flippant QT post about it
https://x.com/BowTiedCaiman/status/1768785556341768369?s=20
“Zeroing” your sights is one of those fundamental things you need to learn how to do with your new rifle, but might not understand the science behind. Here’s a TLDR explanation:
Ballistics 101
As soon as the bullet leaves the barrel of your rifle, it starts falling towards the ground. So if you held the rifle directly parallel to the ground, you would always hit the target below what you’re aiming at. Because of this, bullets actually leave the barrel aimed slight upwards. The point in the distance where the bullet meets the reticule you’re using to aim is the “Zero”. So if I have a 50 yard zero, that means I put my reticule on the target at 50 yards away, and the bullet rises to hit that target exactly where I’m pointing. Illustration to demonstrate
Bullet leaves barrel in a slight upward arc relative to the ground surface. Bullet hits target (Point of Impact) at 50 yards where it intersects with Point of Aim. The “Zero” is hence set at 50 yards.
It’s important to remember the trajectory of a bullet will depend on how fast that bullet leaves the barrel, which in will depend on a matter of factors, like
Caliber
Barrel Length
Bullet weight
Power of cartridge
Note that in that illustration the bullet continues to arc upwards past the 50 yard zero, meaning that it will hit a target *above* the point of aim if it impacts something between 50 and 200 yards. Relative Points of Impact for a typical 50 yard zero using 5.56 shown below
While POI is pretty much the same for 50 and 200 YDS, POI is *above* between them, and then falls below past 200 yards to a gradually more aggressive drop. To hit something past 350 with a 50 yard zero, you need to aim completely above what you’re shooting at!
Before choosing a Zero for your AR-15 or any other rifle, it’s important to consider a couple things
What kind of ammunition you intend to use, and how does that interplay with the barrel length you’re using?
How do you intend to use the rifle? You may find one zero favorable/easier to use than another if you only intend to ever shoot short distances.
What kind of optic are you using, and how high is it off the bore axis of your rifle? The distance between the height of your reticule and the bullet leaving the gun affects what point that trajectory lines up with your line of site. Consult firearm forums if you don’t have the know-how to calculate these things yourself.
If this is interesting to you at all, give me a like before you go down the rabbit hole that is rifle zeroes and ballistics in general. Have a good weekend!