Slide mounted red dot sights are becoming more and more popular on pistols. With the adoption of Carry Optics by both USPSA and IDPA, competition shooters and defensive shooters alike are training with slide mounted optics. Whenever optics enter the equation, the issue of how to zero them always comes up. Whether it’s a rifle or a pistol, you need to zero your red dot sight.
When zeroing a red dot sight, there are three major issues to bear in mind: the changing point of impact with different loads, mechanical offset based on your zero distance, and whether or not you need to co-witness your iron sights. Before we worry about any of that, let’s discuss the two ways to zero your red dot: the 10 yard zero, and the 25 yard zero.
25 yard zero
This is the “traditional” red dot sight zero distance that most people are familiar with and many would assume to be the default. To do a 25 yard zero, you’ll need some kind of rest, and either a spotting scope or a lot of time. The process is simple: shoot a 3 shot group off a sandbagged rest, go downrange (or use the scope), make adjustments, repeat until the gun is hitting where you like. The problem with the 25 yard zero is that it’s time consuming, and it’s less than ideal for close range shooting, which we’ll discuss more.
10 yard zero
This is my preferred method for zeroing, and it’s one I picked up from Scott Jedlinski of Modern Samurai Project. To put it simply, set a target at 10 yards, and standing unsupported fire a three shot group. The goal is to get all three rounds to touch in an area that’s about 1 square inch. It’s simple, it’s efficient, and in my experience it takes far less time than a 25 yard zero, and yet it’s just as effective. It also doesn’t suffer from the issues of mechanical offset that you encounter with a 25 yard zero.
Changing Point of Impact
When zeroing a red dot sighted pistol, the changing point of impact of different rounds is important to remember. If, for example, you’re zeroing a gun for personal defense, you should zero it with your carry ammo, so that you know exactly where the gun shoots with the ammo you’re betting your life on.
Similarly, if the gun is primarily for competition, zero it with your match ammo. Whether that ammo is cheap FMJ or sick handloads, make sure that the rounds go where you want them to go every time. What if your match gun is your carry gun?
In that situation, it’s important to pick a “match” round that is the same or reasonable similar to your defensive round. For example, if your carry 147 grain HST, the Federal 147 grain American Eagle is likely going to produce a similar point of impact to your carry load.
What is mechanical offset? It’s the physical height of your red dot over the bore of your pistol. It used to be that this was only something you had to deal with when shooting rifles, but now with red dots on pistols, it’s a big deal. It’s also why I don’t like the 25 yard zero for pistols. When you zero a 9mm pistol at 25 yards using a red dot, your point of impact at 7 yards can be as much as a foot lower than your dot’s point of aim on the target. In a life or death shooting scenario, I really don’t want to be thinking about how much I need to hold over on the target to get rounds where I want them. One of the ways to help with mechanical offset is to have your slide machined to accept a red dot sight, instead of just mounting it on a plate.
The 10 yard zero on the other hand shoots slightly high at 25 yards, which to my personal preference is a better choice. With the 10 yard zero method, I have a zero that works with no or minimal hold over/under all the way out to 25 yards, without having to adjust for mechanical offset when shooting at real-world self defense distances.
On a pistol whose primary purpose is personal defense, I believe that you should establish a co-witness with your iron sights. What this means is that you’ll likely need to get suppressor height sights which will be visible through the lens of the optic. Assuming that your sights are correctly regulated for your gun and the ammo you’re using, your red dot should rest somewhere in the vicinity of the tip of your front sight once the red dot is zeroed.
I’m a big believer that a defensive pistol should have iron sights. While modern red dots are extremely robust and hard to kill, weird things happen, and having the comforting security blanket of iron sights just makes me feel better about myself. Some modern red dots, such as the Leupold DeltaPoint have an option to have a rear sight included in the sight body.
On a pistol intended solely for competition I’m ambivalent towards co-witnessing. The argument could be made that competition should be taken seriously, and I agree with that, but if iron sights aren’t available or practical for a competition pistol, I am not going to lose any sleep if they don’t have them.
It’s my opinion that when you take all the relevant factors into account, the 10 yard zero is the best choice of zero distances for people who are self defense or recreational shooters. It saves time and ammo, allowing for more practice; and is more practical for real world applications. Remember: 3 shots all touching, standing unsupported at 10 yards.