Many people think of iron sights or red dots at being very limited in precision. In fact, they can be quite precise, especially aperture (“peep”) sights. Good aperture sights are quite a bit more precise than a red dot, and rival most scopes which aren’t’ designed for target shooting. The caveat is that they require an aiming point that you can actually see. In NRA high power competition, good shooters regularly hold 1MOA with iron sights at 600 to 1000 yards. Even novice shooters like myself have little trouble maintaining 2-3 MOA groups at 600 yards with an AR15, on an appropriate target. The NRA targets have aiming points of approximately 6 MOA. While it seems odd that you can hold a large sight post onto a huge, fuzzy aiming point and hit a tiny area in the center of the aiming point, it works! The trick is that you need to have a crisp front sight picture, and align it to the aiming point the same every time. If you try this with aiming points of different sizes, shapes, and colors, your POI will shift all over the place.
The most accurate iron-sight shooters, like Olympic and International competition (50m, 3-sposition, air rifle, etc) use “globe” sights, where the front sight is not a post, but an aperture. This only works with round targets, for obvious reasons – you look through a circle in the rear sight, and then align a ring between that and the target. It’s very easy to get those circles perfectly aligned, and so globe-sights rival scopes for precision. Assuming you have a properly-sized, perfectly round target, that is. Note how easy it is to see that one of the sight-pictures below is offset by one scoring ring when using the globe sight, but that the same mis-alignment is very hard to see with the post. The human eye is very good as lining up concentric circles.
Many High Power shooters in classes that mandate post-type front sights use a “line of white” hold, where there’s a sliver of white target backer visible between the aiming point and their front sight post. They feel this gives them more consistent vertical. However, this is a competition strategy, not a practical application of the sights – if you give them an aiming point of much different size, their POI will shift dramatically. I prefer a center hold, where the top-center of the sight post matches my POI. This is less precise, but won’t change with the target I’m shooting at.
So, there are tradeoffs between being able to very precisely hit a target of known size and shape, and being able to hit targets of varying size and shape. The best thing to do is practice with varying aiming point sizes and shapes, and see how they impact POI, trying to train yourself to truly hold center. But you need a starting point, and that is the bullets impacting precisely on the top-center of the front sight post.
Red dots are similar. I’ve heard people say they can’t be expected to shoot better than 4MOA, because they have a 4MOA red dot. Again, if you have a target that allows you to align the 4MOA dot over the center of the target, there’s no reason you can’t group quite a lot smaller than 4MOA. Also, some people just accept inaccuracy with large dots, because they aren’t designed for precision. That’s true, but having your zero be off by 2-3 MOA isn’t going to do you any favors. Just because you may not have a precise aiming point on the targets you usually shoot at is no reason not to have the bullets landing squarely under the middle of that dot.
So, with iron sights, scopes, and dots, we should choose an aiming point for sight-in that is symmetric, to avoid problems like the line-of-white hold. It should also frame the crosshairs, dot, or sight post in such a way that we can most easily sight-in the weapon so that the POI is directly under the center of the aiming point, whether this is a 10 MOA-wide sight post, a 4MOA blob of a red dot, or a 0.05mRad-wide crosshair. Once sighted-in this way, we’ve eliminated a major variable and can get down to the business of learning how to set that POA on various targets in a consistent fashion.
I’ve developed a set of targets for my own use (available here), which have proven to be the most precise way to get sighted-in with a variety of weapons. For both red dots and iron sights, I use a white circle inside a heavy black ring. A solid black circle also works well for iron sights, but I find the black and white combination to offer a wider variety of sight pictures with various-sized sights, and mitigate some of the effects of changing light, which can make circular targets appear to vary in size. Also, it lets me only keep one set of targets around for both iron sights and red dots. Ideally the edges of the front sight post line up fairly closely with the outside of the black ring. Just a bit wider than the ring seems to be best, so you can get an even amount of overhang on either side. The 100 yard target has the ring nearly to the edge of the paper – I find it works best horizontally, to give some extra white to help frame the post inside.
The red dot sight is centered up inside the white circle. This allows a thin ring of white to be visible between the dot and the black ring. This is like using a globe sight, taking advantage of how easy it is to spot misalignment with circular, concentric shapes. My astigmatism makes most red dots blur off to the side, so I need to crank the brightness down until I can barely see the dot in order to make it crisp enough to line up precisely – experiment with brightness if you’re unable to line the dot up very accurately. Lining up the red dot within a circle this way, it’s very easy to get ~1MOA accuracy with a 4MOA dot. Again, shooting these tiny groups isn’t the point - the point is to get sighted-in as precisely as possible, to remove that variable from everything else that’s going on when trying to take typical red dot shots, which are fast and unstable. You have enough to keep straight in those situations, without worrying about a bad zero!
Scopes are generally very easy to line up – crosshairs are literally designed just for this purpose, and the magnification shows small errors more readily. However, they should still be lined up carefully. Bisecting a circle can be done with a crosshair, but it’s not all that easy to get precise, especially when the circle is very large compared to the crosshair. It’s especially hard when the crosshair is the same color as the circle. Also, many people are now shooting FFP scopes with crosshairs that look rather thick on high magnification, subtending around 0.05mRad. These scopes tend to be on accurate rifles, often capable of shooting groups around 0.1mRad. If you take any sight picture where the crosshair covers the target as “good enough” with those numbers, you’ll add at least 50% to your group size. Just like lining up circles is easy, lining up corners is easy. With the straight lines of the crosshair, it’s best to hit the corners of a diamond. Ideally there will be a small but clear window of white visible in each corner of the crosshair-diamond intersection. I actually draw up these targets by creating simulated crosshair, mimicking the width of the reticle lines at the distance I plan to shoot this target. With a SFP scope, you may even find more precision by backing off on the magnification a bit, to allow crisper framing of the reticle within the diamond.
The next time you hit the range to zero a weapon or collect data on group size or drop, take a moment to ensure that the aiming point on your target is as precise as possible. Having the skills to hit the center of a non-ideal target is important, but eliminating aiming point uncertainty during zeroing or load development is a smart move.