#What the two notch shapes actually are
A quick disclosure first, because it explains why a Mac software person is writing about iron sights at all. I build NotchBay, an app for the notch on a MacBook, and the word notch pulls in searches from a completely different world: the rear-sight notch on a pistol or rifle. So I dug into the real question, checked it against reference sources rather than trusting my own memory, and wrote the answer I wish had been at the top of the forum threads. If you never touch a Mac, this page is still for you.
Both shapes live in the same family: an open sight, meaning a rear notch and a front post that you line up by eye. The only thing that changes is the profile of the cut in the rear blade.
A square notch is a rectangular slot with two straight vertical walls and a flat bottom. The style traces back to the Patridge sight, and it is what most target pistols wear. A U-notch is a rounded trough: straight-ish sides that curve into a semicircular bottom. There is also a V-notch, a shallow vee common on shotguns and dangerous-game rifles, but the live debate is u notch vs square notch sights, so that is where I will spend the words.
The whole game with any open sight is the sight picture: front post centered in the rear notch, equal strips of light on the left and right, and the top of the front post level with the top of the rear blade. How easily your eye can verify those three things is the entire difference between these two shapes.
#Square notch: built for precision
The square notch wins on reference points. Two vertical walls give you two clean light bars to balance, and a flat top edge on the rear blade gives you a hard line to level the front post against. When you can see all four of those edges clearly, you can repeat the exact same alignment shot after shot, and repeatability is what a tight group is made of.
That is why bullseye and precision shooters overwhelmingly run a square notch paired with a square front post. Same shape front and rear, so the light bars on the sides and the gap at the top read as clean geometry. If I were setting up a range gun purely to punch small groups off a bench or slow fire, I would want a black square notch and a plain black square post, no dots, nothing distracting.
The cost is honest to state. Square notches are slower to acquire in a hurry, and against a busy background those crisp edges can get lost. In low light with a plain black rear, you are hunting for the front sight. That is a real drawback the moment the shooting stops being deliberate.
#U-notch: built for speed
The U-notch is built around one idea: get the eye to the center fast. A rounded trough naturally cradles a round front dot. Your eye is very good at spotting a circle inside a matching curve, so the sights snap together quickly under stress, in movement, or when you are not taking a careful, squared-up stance. That is the whole reason it shows up on so many defensive and carry pistols.
There is a known weakness, and the ranking threads about this topic circle it constantly: vertical precision. A U-notch has no flat top edges beside the front post to level against. You judge elevation by how much of the front dot sits above the curve, and that amount is easy to vary from shot to shot. Pair a round dot with a rounded notch and you get a fast sight picture with a slightly fuzzy top reference. For a threat at across-the-room distance, that is a non-issue. For a two-inch group at 25 yards, it costs you.
So U-notch sights are genuinely good, just for a different job than the square notch. Fast, forgiving, defensive: yes. Surgical, deliberate, benchrest: not their strength. Anyone who tells you one shape is simply better than the other is skipping the question of what you are actually shooting.
#The front sight decides more than the notch
Here is the part most of the square-versus-U arguments underweight. The rear notch is only half the picture. The front sight, its width, its shape, and whether it carries a dot, changes the outcome more than the notch profile does.
| Pairing | Feels like | Best for |
|---|---|---|
| Square notch + square post | Precise, deliberate, slower | Target, bullseye, slow fire |
| U-notch + round dot | Fast, forgiving, less exact up top | Carry, defensive, speed |
| Square notch + round dot | Balanced, common on carry guns | General purpose duty and carry |
| U-notch + square post | Uncommon, mixed references | Rarely chosen on purpose |
Generalizations, not laws. Individual eyes, lighting and sight radius shift all of this.
Two other variables swamp the notch debate in practice. Sight radius, the distance between front and rear sights, does more for mechanical precision than any notch shape: a longer radius makes the same angular alignment error smaller at the target. And front sight width relative to your light bars determines how finely you can center. A thin front post in a wide notch gives you generous light bars and fast centering; a fat post in a tight notch gives you precision but a slower, fussier picture. Pick those two before you agonize over square against round.
#So which should you pick?
No hedging. Here is how I would actually decide.
- Range gun, groups matter, no clock: square notch, square front post, both black. Maximum reference edges, maximum repeatability.
- Carry or defensive gun, speed matters: U-notch or a plain square notch with a single bright front dot. Prioritize a front sight you can find instantly, and blacken the rear so nothing competes with it.
- One gun that does both: a square notch with a fiber-optic or tritium front dot is the sensible compromise. You keep the crisp rear edges for aimed shots and still get a front sight that jumps out fast.
- Bad eyes or old eyes: stop optimizing the notch and consider an optic or an aperture. More on that next.
The mistake I would avoid is treating this as a moral question. It is an ergonomics question with a use case attached. Match the sights to the shooting, not to whichever camp is loudest in the thread.
#Where notch-and-post sights stop
Both shapes share one fundamental limit: a notch-and-post sight asks your eye to hold three things in focus at once, the rear notch, the front post and the target, when the eye can only truly focus on one. That is why the whole square-versus-U debate has a ceiling. Past a point, changing the notch shape cannot fix the underlying compromise.
Two designs step around it. An aperture or peep sight replaces the rear notch with a ring you look through, and the eye auto-centers the front post inside it without conscious effort, which is why many shooters find peeps the most forgiving iron sight for both speed and precision. A red dot or scope goes further and puts a single aiming reference on roughly the same focal plane as the target, removing the notch entirely. If precision at distance is the goal and budget allows, an optic beats any iron sight, square or U. That is worth knowing before you spend an afternoon filing a notch to chase a problem a different sight would erase.
The other kind of notch
Since some readers did land here from the software side, a quick bridge before the FAQ. The notch on a MacBook is a fixed cutout, not something you align by eye, and the useful analog is the same: a small fixed slot is only worth having if you put a clear reference in it. If that is the notch you meant, the honest starting points are whether the free Boring Notch app is safe to run and how the Mac menu bar works around the cutout. Different notch, same principle: the shape is nothing without what you put in it.
#Frequently asked questions
Are U-notch sights good?
Yes, for the job they are built for. A U-notch guides a round front dot into the center quickly, so it shines for defensive shooting and fast target acquisition. The trade-off is vertical precision: because the rounded notch has no flat top edges to level against, judging elevation is less exact than with a crisp square notch. For a carry gun, that is a fair trade. For deliberate bullseye groups, a square notch has the edge.
Which type of sight is most accurate?
For raw precision, an optic wins: a magnified scope at distance, or a pistol red dot up close, because there is a single aiming point on the same focal plane as the target. Among iron sights, an aperture or peep sight is the most forgiving, since the eye auto-centers the front post inside the ring. Between open-sight notch shapes, a square notch paired with a square front post is the most precise for slow, aimed fire.
What sights does the FBI use on Glock?
The FBI's Glock pistols are commonly reported to ship with Ameriglo sights specified for the contract: a single tritium front dot ringed with a bright luminescent outline, over a plain, blacked-out serrated rear notch. The design is deliberate. One glowing front reference and no rear dots keeps the eye on the front sight, which is where accuracy comes from. Confirm current specs from Ameriglo and FBI sources, since contract details change.
What are the three types of sights?
The usual grouping is open sights (a notch-and-post, where U-notch and square notch both live), aperture or peep sights (a rear ring the eye looks through), and optical sights (red dots and magnified scopes). Open sights are simplest and always on. Aperture sights are faster and more forgiving for the eye. Optics are the most precise but add cost, batteries and bulk.
