What does a pistol red dot height checker measure?
It compares the optic window floor, any adapter-plate height, and the iron sight height to estimate where the irons appear in the red-dot window. The result is a co-witness band such as no witness, lower fifth, lower third, busy, or too tall.
What is a co-witness red dot for a pistol?
A co-witness setup is one where the iron sights are visible through the red dot window when the dot fails or the battery dies. The irons sit tall enough that the front post lines up with the rear notch inside the optic's glass. On a pistol that needs taller irons than the factory set, often called suppressor-height or optic-height sights. Without them the irons sit below the window and offer no backup reference.
Should a pistol red dot co-witness?
Yes for a fighting or duty pistol, optional for a range or competition pistol. Co-witnessed irons are a no-thought backup if the dot washes out, the lens fogs, the battery dies, or the dot is occluded by rain or blood. The trade-off is a slightly busier sight picture and the cost of suppressor-height sights, usually $80-$150. Competition shooters often run a clean optic with no co-witness to maximize window real estate.
What's better, absolute co-witness or 1/3?
Lower 1/3 co-witness is better for most shooters. The irons sit at the bottom third of the optic window, keeping the upper two-thirds clear for the dot and the target. Absolute co-witness puts the front post dead center on the dot, which is faster to confirm under stress but clutters the sight picture during normal shooting. On pistols, lower 1/3 (or lower 1/5 on micro optics) is the dominant choice. Absolute is more common on rifles with backup iron sights.
Will factory Glock 43X MOS sights co-witness with an EPS Carry?
Yes, usually as a shallow backup reference. On a Glock 43X MOS, factory slimline sights can be usable through an EPS Carry or SCS Carry on a thin RMSc-to-K plate, but they are not a tall lower-third sight picture. Choose verified optic-height slimline sights if you want more front sight in the window.
Is lower-third co-witness always better than lower-fifth?
No. Lower-third irons are easier to pick up if the dot fails, but they can clutter a small carry-optic window. Lower-fifth keeps the dot view cleaner while still leaving a backup reference if the sight set is tall enough.
Why are some sights excluded from recommendations?
The tool only recommends sights with verified numeric dimensions. Catalog products remain visible when fitment is relevant, but unknown front, rear, optic, or plate heights are marked as missing instead of guessed.
Does suppressor diameter change the recommendation?
Not yet. The suppressor control is a schematic overlay only because reliable clearance math also needs source-tracked bore height and suppressor centerline data. The sight recommendation is still driven by verified optic, plate, and iron sight heights.