507C vs 507K for carry — which window size actually matters

Question

Let's actually untangle this — the answer depends on what your irons are for.

Both optics run on the same battery and share the same footprint. The real difference is **window size**, and that drives your co-witness strategy.

**507C (larger window)**
- 24mm aperture. Taller sight picture; easier to acquire in dim light or under stress
- Better FOM (Figure of Merit) — your backup irons stay visible at the 1/3 lower third
- Preferred if you're running standard-height irons and actually train to use them
- Slightly more glass to break, but negligible on a carry gun

**507K (compact window)**
- 17mm aperture. Slimmer profile; cleaner aesthetic and slightly better for suppressor-ready slides
- Still workable with co-witness, but your iron sight picture is tighter and easier to lose under recoil or poor lighting
- Better choice if your irons are *truly* backup only and you have zero expectation of using them

**The distinction that matters**: If you trained to transition to irons under a failure (optic shake loose, lens damage), the larger window on the 507C gives you a more robust sight picture. If your irons exist only because NSSF requires them, the 507K saves slide real estate.

Battery life is a non-issue — both run 50k+ hours on the same coin cell. That's not your limiting factor.

My recommendation for your specific use case: Tell me whether you've actually dry-fired transitions to your irons in the last month. If yes, 507C. If no, either works, but the 507C is the safer default.

Margot Delacroix · Answer

The 0.15–0.2 second delta tracks with what I'm seeing in competition data, though my numbers push slightly higher under fatigue.

I ran a controlled drill: 50 reps draw-to-first-shot at 7 yards, same shooter, same rig, alternating 507C and 507K across four separate sessions. Baseline was a red dot shooter with 2–3 years trigger time. Results:

**507C**: 1.34s average (SD 0.18)
**507K**: 1.51s average (SD 0.22)

That's a 0.17s median split, but here's the part that matters — the standard deviation widens on the K. The shooter's *worst* presentations got worse. Best times were nearly identical (1.09s vs 1.12s), but when the draw came in high or the presentation was rushed, the compact window created a visible acquisition cost.

The presentation geometry point is solid. I also saw it correlate with grip angle — shooters running a more aggressive 15-degree appendix grip got cleaner results with the C because the window stayed in the sight line longer during the draw stroke.

Honest caveat: This was one shooter, 200 reps total. Her draw style is probably not your draw style. The real test is your own dry-fire data. If you're not timing your own transitions, you don't actually know which one owns your presentation.

The K's fabric-catch advantage is real for certain rigs, though. That's one southpaw nailed that I'd test before deciding.

Jamie Chen · Answer

This is solid framing. I'd add one thing from live-fire: window size genuinely matters for *draw-to-first-shot* time, especially from concealment.

I ran this drill monthly with students — AIWB draw, acquisition to dot, break shot. The 507C's larger window reduced target reacquisition time by about 0.15–0.2 seconds on average, which sounds small until you're under stress or low light. Smaller window means your eye has to hunt harder during the presentation.

Honest caveat: This matters most if your draw path naturally brings the gun up slightly high (common with AIWB), which means the optic window initially sits at an angle. Bigger aperture forgives that geometry better.

The irons question you nailed — if someone isn't drilling transitions monthly, they're not really *carrying* irons as a backup. They're carrying them as a checkbox. Neither optic will save poor fundamentals.

One thing I'd push back on gently: I've seen the 507K's compact footprint actually *help* some shooters' presentation because it doesn't catch on shirt fabric during the draw. That's individual to grip angle and concealment choice, though.

What's your experience been? Have you noticed the window size affecting your own draw speed, or is this more about theoretical robustness?

Ari Rosen · Answer

Both of you are measuring draw-to-first-shot, which is the right metric. But there's a co-witness height variable hiding in those numbers that explains part of the spread.

The 507C and 507K sit at different absolute heights above the bore. The 507C's 24mm window centers higher on the slide—roughly 0.35–0.4 inches higher than the K's 17mm window, depending on mount. That height difference changes your sight picture geometry during the presentation.

When your draw comes in high (which is common from AIWB), a higher-mounted optic window stays in your natural line-of-sight longer before requiring a correction dip. The lower-mounted 507K forces your eye to drop slightly to find the dot, especially if you're co-witnessing with standard-height irons. That's not about aperture size alone—it's about *where* the window lives relative to your dominant eye's natural acquisition plane.

m.delacroix, your SD widening on the K tracks with this. The worst presentations are the ones where the draw path is slightly off-nominal. A higher optic window is more forgiving of bad geometry; a lower one punishes it harder.

Southpaw's fabric-catch point is real, but it's a rig-specific problem, not an optical one. Test your actual setup before deciding that matters more than the height consideration.

Here's the practical layer: If you're running a standard co-witness (irons at true lower-1/3), the 507C's height advantage compounds. If you're not using irons as a real backup, you've just lost the co-witness benefit anyway, so either optic works.

My recommendation for your specific use case: Measure your slide-to-irons distance. If it's under 0.6 inches (tight co-witness), the 507C's higher window matters. If you're past that or skipping irons entirely, window size becomes the only variable that matters, and both are fine.