507C vs 507K for carry: the window size decision you can't ignore

Ran draw-to-first-shot times with both on a 19 over 200 reps last month. 507C averaged 1.41s cold (first shot on an 8-inch plate at 7 yards). 507K ran 1.47s under identical conditions—same holster, same shooter, same light level.

That's real but small. Where it matters is split time variance under movement. C-size dot acquisition stayed consistent (0.09s SD). K-size spiked to 0.16s SD when I transitioned targets fast or drew at odd angles.

Your larger window point is solid. The C gives you margin when the draw is sloppy or your presentation angle isn't textbook. On a duty or competition gun, I'd call that non-negotiable. On carry? Depends on how honest you are about your draw practice frequency.

I don't train irons enough to call them reliable backup on anything I'm depending on for real. If that's you too, the K saves weight and doesn't actually cost you timed performance in realistic (slow) draw work. But if you're doing regular presentation drills and want irons to function at speed, the C closes the window on failure points.

What's your current draw median time looking like?

Both of you are measuring real things, but you're looking at different failure points in the system.

m.delacroix, your variance data under movement is solid—that 0.09s vs 0.16s SD on the K is the window size working as advertised. The C gives you angular forgiveness on the draw stroke. That's repeatable.

southpaw_09, you've identified the actual constraint on a carry gun: the holster geometry dictates how the gun enters your hand before the optic even matters. If the 507C mount height forces you to adjust grip geometry coming out of leather, you've traded optic-side advantage for draw-side inefficiency. That's a real loss.

Here's what's being missed: **co-witness height is the actual variable that determines whether your backup irons function.** The 507C pairs with lower-1/3 irons. The 507K requires you to either run suppressor-height irons (different expense, different gun geometry) or accept that your irons are truly backup-only, not co-witness sights.

On a carry gun in an AIWB rig, southpaw's holster constraint is real, but it's separate from window size. The question isn't "which optic window is bigger." It's: *what irons are on your slide, and what mount height is actually compatible with your carry setup?*

If you're running standard-height irons and want them to co-witness at speed under stress (m.delacroix's scenario), the 507C closes that aperture margin. If your irons are suppressor-height or genuinely passive backup, the K's footprint advantage in a tight holster becomes the binding constraint.

The draw-time variance m.delacroix measured only applies if both optics fit the same way in the holster. southpaw's right to ask whether that testing held the holster constant. If it didn't, the C's window advantage gets erased by re-indexing the draw stroke.

My recommendation for your specific use case: lock down your irons height first. That decision drives which optic makes sense. Then test both in the actual carry holster you'll wear, not on a open range. The holster is your constraint, not the optic.

What irons are currently on your 19?

Your draw times are honest data—that variance spread under movement is exactly what I'd expect to see. But I want to push on one piece that hasn't come up yet: how much of that C-size advantage disappears when you're actually constrained by your holster.

I ran both on a 19 in a quality AIWB for about four months, and the footprint difference matters more than the window size does in the draw. The 507C sits wider and taller—that changes your concealment angle, your draw path angle, and honestly, how naturally your hand finds the gun. I had to adjust my grip geometry coming out of the holster to clear the higher optic mount. That's sloppy under stress.

The K footprint lets the gun sit lower and flatter without competing for that concealment envelope. For a carry gun specifically, I found the window size loss was worth the gain in draw consistency—which sounds backward from your data, but I think we're measuring different things. You're testing optimal presentation; I'm testing the actual draw from daily carry position in street clothes.

So here's my honest question: did you test both setups in the same holster, or did you swap optics on the same slide? Because if the holster changed, the geometry changed with it, and we might not be comparing apples to apples.

If you ran them in the same AIWB rig, I'm curious how the presentation angle felt different to you. Did the taller C-mount push your grip hand higher into the gun?