Red dot sights are primarily made for close range shootings, but with the right MOA dot sizes and magnification it can be used very effectively for long range shooting up to 300 yards, even if you have astigmatism.
MOA Selection
For long range shooting with a red dot sight
a 1 or 2 MOA dot size is preferred.
A ring reticle is helpful to estimate target range with known target size, but a single dot works just fine for combat effective hits.
They are small enough to give the shooter more precise aim and they don't clutter up the sight picture, so the shooter can see the target clearly.
This is even more important for low light shooting. With enough magnification and dot clarity aiming with a red dot sight will get the rounds on target.
Brightness Control
When shooting long distance with a red dot sight especially in low light conditions, bring down the brightness setting to the point where there is no emitter starburst can help you aim better.
This is what you don't want when shooting long range with a red dot!
Reticle glow is obscuring targets and surrounding objects
Magnification
Adding a magnifier scope behind the red dot is the best way to extend the capability for your red dot sight.
The most popular are the 3X, 4X and 6X. 3X is the most popular for most use cases without getting ridiculously expensive.
3X magnifier provides the best light emission to give you a brighter image, and it gives the shooter good eye relief and eye box. So there is more head flexibility.
Unlike a 6X magnifier, the eye box is very tight and its almost like a low power variable optic.
The intended use case for a red dot sight for long range isn't to compete with long range precision shooting to get a half MOA shot group.
It's more about identify target at long distance and send rounds down range to get combat effect hits if the dot is zeroed correctly.
