More and more people are making the big shift from using iron sights on their pistols to the electronic red dot optic. Many of them don't realize how to best use this technological advantage. Hopefully, this will help you get started.
This tutorial is not the end-all-be-all bible of red dot pistol shooting. I'm just trying to convey the basic visual concepts to help you get started. When someone comes to one of my classes with a dot on their pistol, they will often be using the sight in a manner that completely negates the advantage of having the dot.
Most people learned to shoot handguns, and rifles for that matter, with iron sights. The system is simple. Align the top of the rear sight with the top of the front sight with the center of the target. Shooters were taught to create this sight picture by keeping the front sight clear in their vision while the rear sight and target become blurry. The last part of this description is what is most important to change.
Finding the Dot
It can be difficult to find the dot in the window at first. This is what takes the most practice. You will have to train yourself to always have your hands in a certain position so that the dot is instantly visible when you raise the gun to your eye. A sort of "muscle memory" will develop. If you raise the gun, the dot is usually high and you need to point it more down. A little trick to start getting consistent is to find the front sight through the window of the red dot and try to align it with the rear. You won't be able to because the optic is in the way, but if you continue that downward tip of the muzzle, the dot will appear in your window. Then continue practicing raising the gun, or drawing from a holster, and see the dot in the window every time.
Sight Picture with a Red Dot
When you aim a red dot sight at a target, first look at the target with both eyes open so that it is the clearest thing in your vision. Then, without breaking that focus on the target, raise the gun in front of your face so that the dot is in line with your dominant eye as it looks at the target. The dot is the impact point of the bullet so look at the exact spot you want to shoot and place the dot over it. (Notice in the photo below that the stickers on my safe are clear while the gun appears blurry. This is what it should look like.)
When you aim a red dot pistol with both eyes open, you can then look at targets, place the dot on them, and fire. If you are closing an eye to shoot with a dot, you are making it harder to see and shoot. If you find this challenging, another great trick to try is putting a piece of tape over the front of the optic (so that you see the dot but not the target through the window). Then aim at targets and shoot. This will help train your eyes and brain to shoot target focused.
Do not stare at the dot on the target, look at the target with the dot on top of it.
Co-Witness Iron Sights
Co-witness iron sights are popular, but I find them to be a hindrance. Initially, it will be nice to have them there to help you find the dot, but as you get better at shooting with the dot, you will likely find that the irons, especially the rear sight, will get in your way. If you want irons as a redundancy to the optic, I would find irons that align in the bottom third or bottom quarter of the window. That way they aren't in your way when you are shooting the dot.
I have a Langdon Tactical RDO slide on my competition gun. It comes with irons that co-witness for a Trijicon RMR, but are at the bottom third of the window so when the dot is centered in the window they aren't in the way. I initially had a Holosun on this slide and hated the irons being right in the middle of the window. (See photo below)
Dots are Better Than Irons
Once you get the hang of how the dot works, they are a faster and more accurate sight system than irons. It's just not possible to line up your eye with three things as quickly as it is to do it with two things. Are they less reliable than irons? In my experience, yes, but only slightly. I've had iron sights drift or had a screw come loose even when Loc-Tite was used. And I just got my Holosun back from a warranty replacement after the emitter for the dot refused to go up to its full brightness. I've owned five slide-mounted optics and have only had that one fail, though the ring reticle was still working and thus the optic was still functional.
In terms of reliability, if I was carrying a red dot gun as a police officer, I would only use a Trijicon RMR or SRO, probably an RMR. From what I have seen they are the most bulletproof optics that put up with being shot 30,000 times or more and keep on trucking. They aren't all perfect, but they have the best track record so far. I like the Deltapoint Pro by Leupold, but the battery life is not great compared to the virtual eternity a battery lasts in a Trijicon or Holosun. I've only changed batteries in those out of paranoia, not because they were dead.
If you want a cheaper one to try out, the Burris Fastfire III functioned well on my Glocks for a year. One had 5,000+ rounds and the other had around 3,000. The brightness settings are limited and battery life isn't great but it isn't bad. The Vortex Venom is another cheaper one to try, but do not get the Viper. There are a lot of other pistol dots out there but I don't have an opinion on them since I have not used any of them.