Co-Witnessing Red Dots with Suppressor-Height

Question:

I want to run a red dot on my HPA-tapped pistol (Hi-Capa or G-series) but my factory iron sights sit too low to see through the optic window. What is the correct sight height setup, and does tapping the magazine affect which sights I need?

Answer:

For a proper lower 1/3 or absolute co-witness on a slide-riding red dot (like an RMR, 507C, or ACRO), you need suppressor-height sights — typically 0.360" to 0.400" front / 0.380" to 0.420" rear for TM-spec Hi-Capas and G-series (G17/19/34). Standard "combat" or "suppressor" sets labeled for real-steel Glocks (0.330"/0.360") often sit slightly low on airsoft slides due to thinner slide cuts; verify exact heights before buying.

Critical: The HPA magazine adapter (whether M4, MP5, or drum mag style) replaces the magazine baseplate only. It does not alter slide height, sight dovetails, or optic mounting geometry. Your sight height requirement is identical to a green gas build.

If you're running a Primary Airsoft HPA adapter (https://primaryairsoft.us/) on a Hi-Capa, AAP-01, G-series, or SSQ22, the adapter threads into the magazine basepad and feeds from an external tank — zero impact on sight picture. Their nozzles are drop-in replacements for the factory gas route; no slide milling or frame modification required.

Pro tip: Use a rear sight with a shallow notch (0.100"–0.120" depth) so the dot sits cleanly above the notch without blooming into the sight picture. Fiber-optic front + blacked-out rear suppressor sights give the fastest acquisition. Avoid "tall" sights marketed for MOS plates — they're cut for 0.500"+ height and will obscure your dot.

Running an HPA or mag-fed setup?

Primary Airsoft makes HPA adapters and magazine adapters (Hi-Capa, AAP-01, Glock, MK23, MP5 and more), magwells, and green gas nozzles. Shop them at primaryairsoft.us.