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Red Dot Optic Targeting Considerations and Calculator

The main purpose of this article is help explain the relationship between optic sight height and targeting.
There is a RDO target accuracy calculator at the bottom of this page.

Red Dot Optics are also referred to as Reflex Sights. This document will refer to them as RDOs. The Red Dot name came from a time when all the reflex sights all had red dots. Well, now they have sights with green dots as well. However, I have never heard a green optic referred to as a GDO (Green Dot Optic).

Over time RDOs have come down in price and increased in sophistication and reliability. Recently they have really come into their own. At one time, you mostly saw them on rifles but now they are commonly seen on handguns. Using an RDO makes it much easier to aim your handgun at a target. With an RDO sight the dot is projected onto a transparent optical surface and wherever you see the dot on a target is where the bullet will go. With traditional sights, there are three different planes, the rear sight, the front sight, and the target. This is a far more challenging eye exercise than placing a dot on the target. If you have iffy eyesight or aging eyesight, the RDO can make it much easier to shoot and make you a better shooter.

As with all things in the gun world, there are pros and cons to everything. There are also a variety of opinions. Many say a shooter will become faster acquiring targets with and RDO but there are also those who also say they are faster with traditional sights. Depending on circumstances and the shooter, they are both correct. Some say RDOs can fail at any time and you must have co-witness sights. This is true to a degree but battery life is many thousands of hours and their reliability today is incredible. Personally, I do not worry about reliability. It is not the purpose of this article to wage into all the debates over RDOs. This article was written to help in understanding the relationship between optic height over bore and targeting.

The RDO Sight Angle Effect on Targeting.

Since the RDO sight sits significantly above the bore center, a viewing angle is created when it is zeroed in, usually at 20-30 feet. Therefore, when sighting a target further away, say 100 feet, the barrel of the gun will be raised by putting the RDO sight on the target. The viewing angle and distance to the target creates a variable delta between the sighted target and the trajectory of the bullet. This causes the impact to be high. The lower the sight the smaller the angle resulting in a smaller delta between the sight line and the bullet trajectory. This sight viewing angle and target distance are used to calculate the difference between the sight view and the bullet impact. By being aware of the effect of shooting distance significantly beyond the sight zeroed distance, you can maintain your accuracy.

RDO Sighting / Accuracy Diagram

RDO Targeting Calculator

You can use the RDO Targeting Calculator to view a reasonable approximation of the effect of RDO height on bullet impact on a target at distance greater than the sight zeroed distance. The result will be close but not exact due to variations in measurements and ballistics. Bullet ballistics are not included in the result. However, at most distances used for handguns, the bullet trajectory can be considered to be flat.

Once values are entered they can be modified and recalculated by clicking on Calculate.


Last revised: January 10, 2022
Author: Steve Gill PistolThoughts.com