We’ve talked in the past about how to zero a rifle. Now it’s time to talk a little about why everyone uses a 100 yard zero, and not a different distance. We have touched on this a little in the prior article but I’m going to explain it in greater detail with this article. I’m speaking primarily of precision rifles here. You may hear your buddies that shoot with an AR15 using a 50 yard or “battle zero” with their rifles. I’ll talk a bit about that as well since AR15s are a popular rifle and this is a rifle website. For a precision rifle, though, with an optic capable of external adjustments, the 100 yard zero is king!
Why a 100 yard Zero?
The biggest reason most people run a 100 yard zero? Everyone else does. Human beings are creatures of habit, and we tend to follow the herd most of the time, that’s where the “sheep” analogy comes from. So when people do any reading on the subject of what distance to zero their precision rifle, the answer most frequently found is the 100 yard zero. Most people never look farther than that. That’s the answer to the question, few people concern themselves with the why behind the answer. That’s what we’re going to discuss in more detail. The why behind the answer. This way, you as the educated reader, know more about why we do what we do in the Precision Shooting sports.
The real reason for the 100yd zero has two main components. The first of which is angular measurement. We’ve all heard the term “minute of angle” before. The loose translation of minute of angle, or MOA, is 1 inch at 100 yards, 2 inches at 200 yards, 10 inches at 1000 yards, and so on and so forth. If all our measurements, whether we’re discussing accuracy of a rifle or size of a target, revolve around the system, why not our zero? We measure group size and accuracy at 100 yards, so that’s a logical spot to start zeroing the gun. Then you know, if your rifle shoots half MOA at your zero, and your point of impact matches point of aim, you’ve got a solid zero and the rifle is performing as expected.
The second component, and the most important, is atmospheric conditions and how they affect the ballistics of your rifle. The simple explanation is that at 100 yards you have established a zero where any changes in your environmental conditions will be rendered inconsequential. If you zero your rifle at sea level in Florida, then get on a plane to shoot a rifle match in Wyoming at 5000ft, there’s a decent difference in your environmental conditions and your density altitude between those locations. With a 100yd zero the shift in point of impact should be minimal.
Downsides of Longer Zeros
Somebody will ask, so we’re going to cover it. Why not use a longer zero? What if you’re shooting ELR distances and your setup doesn’t allow for a 100 yard zero? My suggestion is that you consider altering your setup to allow a 100 yard zero if you can’t do it already. You have two rather large issues with zeroing a rifle at a distance beyond 100 yards. The farther you push your zero out, the more the changing atmospherics can alter your point of impact. So in the same example of a Florida home base and a trip to Wyoming, but with a 500 yard zero, the change in density altitude will alter your point of impact and you zero will be off. Yes, you could record the differences, and be better prepared for the same eventuality in the future.
The Wind becomes your next problem. If you zero your rifle at 500 or 600 yards, how much of your adjustment was wind? Was the base on the receiver a little off axis? Was the scope mount installed correctly? Or was there a stiff wind from the left or right of your shooting position? The problem at 500 yards is that you really don’t know. You don’t know how much of your windage correction was from the wind, alignment of pieces of your rig, or what! There are ranges these days that have 100 yard rifle lanes that are completely enclosed. That’s your ideal spot for zeroing the rifle, 100 yards, and zero influence from the wind.
I said I’d mention the AR15 and battle zeros, so here goes as we wrap up. The point of a 50 yard battle zero is maximum point blank range. The idea is to zero the gun, with a sight or optics that you don’t dial later. When zeroed you want the point of impact to be close enough to the point of aim to achieve hits. In the case of a battle zero, we’re talking about bad guys, human beings. Most 223/5.56 ammo, with a 50 yard zero, is within +/- approximately 2-3″ from the point of aim out to 200 yards. 200 yards is a fine zero for a battle rifle and most combat scenarios.
However, this is a long range, Precision Shooting Sports website. We, and our readers, shoot beyond 200 yards all the time. So setting up the gun for adjustment free shooting for our purposes doesn’t make much sense. For one, our optics are adjustable, if we need to shoot at 500 yards instead of 200, we turn a dial and aim for the center. The 100 yard zero makes the most sense for what we do. It’s a range that’s close enough to negate changes in the zero itself from atmospheric changes. It’s also close enough that the wind at that range has essentially zero impact on the bullet’s flight path, so you can be reasonable sure your zero wasn’t influenced by the wind. As always guys, if you have a question or something to add, please do so in the comments below!