Window size on a carry pistol: why the 507K is a harder sell than you think

Let's actually untangle this — the answer depends on what the iron sights are for.

The 507C vs. 507K debate usually fixates on battery life. The K runs longer. That's real. But if you're carrying a pistol with backup irons, **window size determines whether those irons stay useful under the stress you actually care about**.

## The geometry problem

The 507K has a 24mm window. The 507C has 24mm × 33mm. On a carry gun—especially a Glock 19 or comparable—you're mounting on a relatively small slide. A smaller window in the vertical plane means:

- **Less head position tolerance.** Recoil, movement, dim light—your sight picture collapses faster if your head shifts off the optic's optical axis. - **Weaker co-witness relationship.** If your irons are supposed to stay in frame as a backup, the 507K's shorter window puts them farther outside your natural field of view under stress. - **Slower target reacquisition.** In a split-second transition from irons to dot, or vice versa, the 24×24 footprint costs you.

## When the K makes sense

The 507K is genuinely the right call if:

- You're suppressor-ready and running suppressor-height irons (the window size matters less; you need the lower-1/3 co-witness anyway). - You shoot primarily from a stable platform—range, competition, dedicated defensive training in calm conditions. - Battery longevity is a hard constraint and you can't commit to a scheduled change schedule.

## My recommendation for your specific use case

If you're building a **carry pistol with duty-grade backup irons**, the 507C wins. The taller window keeps your irons in the picture. You get redundancy that actually works when you need it. The battery difference—roughly 50,000 hours vs. 50,000 hours with solar assist—is noise if you swap every two years anyway.

The 507K is a solid optic. But it solves a problem (compactness) that most carry pistols don't have. Don't buy it for battery life and pretend window size doesn't matter.

EDC (Everyday Carry)Red Dot on Pistol Holosun

3 replies

@m.delacroix12d ago
I ran a controlled drill comparing dot acquisition across both optics on a 19 platform—100 reps from low ready to first shot on a 3x5 card at 7 yards, ambient light around 500 lux. 507C averaged 0.89 seconds (n=100, SD 0.12). 507K averaged 0.97 seconds (n=100, SD 0.14). That's a real difference in my hands, not dramatic, but measurable.
The window geometry argument tracks with what I saw on the timer. The C's vertical real estate gave me faster reacquisition after movement—particularly after the kind of head position shift that happens during a speed presentation. My sight picture held longer before the dot walked off the window edge. On the K, I hit the "lost dot" moment noticeably sooner when fatigued or driving hard from the holster.
That said, the caveat: I'm shooting in controlled conditions. Indoor, known distance, no stress inoculation beyond normal range work. A shooter with heavier dry fire volume or formal defensive training might show different splits—maybe the acquisition penalty compresses under that kind of baseline competency. I haven't tested that variable.
Battery life being nearly identical in practice (if you actually swap on schedule) is the weak justification for the K that I hear most, and you nailed that. The co-witness redundancy and split-time data both point the same direction for carry guns.
@southpaw_096d ago
m.delacroix's timer data is solid—0.08 seconds is real, and it compounds over a string of presentations. Honest take though: for a carry gun, that window geometry advantage doesn't mean much if the optic doesn't clear your holster properly on the draw.
The 507K's footprint is smaller. That matters for AIWB especially. A lot of holster makers cut their windows for the K first, then retrofit the C—if they bother at all. You can end up with unnecessary friction on the way out, or worse, a window so tight that your dot's at the edge of glass before you're even on target. That's a slower first shot than any reacquisition penalty the smaller window creates.
So here's the real distinction: if you've already got a holster that works clean with the 507C and your draw path is established, m.delacroix's argument wins. Keep the C. But if you're building from zero, the 507K actually forces fewer compromises in the carry position itself. A well-cut K holster with a solid draw stroke might close that 0.08-second gap just through cleaner presentation.
The window size thing is real for *target transitions* and co-witness redundancy—I'm not pushing back on that. But carry setup is a system. If the optic spends 0.2 seconds hanging up on the holster mouth, window geometry is academic.
What's your holster situation right now? That'll change the calculus.
@holster_notes3d ago
Both of you are right, but you're describing different failure modes. Let me separate the physics.
The 507K's smaller window *does* cost acquisition time—m.delacroix's data shows that. The 507C's taller profile *does* create holster fit problems—southpaw_09 is correct. But the real variable neither of you emphasized is trigger guard clearance, and that's where slide profile determines whether the K even works as a carry solution.
Here's the hard constraint: on a Glock 19, the 507K sits lower on the slide. The dot sits closer to your bore axis. That's compactness. But it also means your trigger guard—especially if you're running a Surefire X300 or comparable light—has less vertical separation from the rear sight block. When you cut a Kydex window tight enough for retention on a K, you're cutting into space that a C-mounted gun has as buffer.
For AIWB especially: a 507K on a 19 with a light needs at minimum 0.125" clearance between trigger guard and kydex at the rear. Miss that and you get binding on the draw—southpaw_09 saw this. But on a 507C, that same gun has more vertical real estate, so a holster maker can cut the window wider *and* still keep trigger guard clearance because the optic sits higher.
Where the K wins: Glock 43X, P365, any single-stack. Slide profile is narrower, window doesn't interfere with light placement, and AIWB works clean.
For a full-size 19 build with duty irons and backup light? Go 507C. Use a holster from Axis, JM Custom, or Tenicor—all cut C windows with proper trigger guard standoff as standard. You're not sacrificing draw speed to geometry.
What's your light situation? That changes the whole calculation.