MOS plate vs mill: which holds zero better on a carry Glock after years?

Question

Let's untangle this — the answer depends on how the gun lives.

**MOS plate system:**
• Adds a mechanical interface between slide and optic mount
• Each interface (plate-to-slide, optic-to-plate) can accumulate play over time
• Easier to replace or swap optics without committing the slide
• Zero shift risk increases if plate screws loosen; requires periodic check

**Direct mill:**
• Removes the plate interface entirely
• Optic mounts directly to slide material
• Fewer mechanical joints = fewer failure points
• Permanent — re-zeroing means permanent slide material loss

**What the data shows:**
 Both systems hold zero reliably on carry guns *if maintained*. The MOS advantage is reversibility; the mill advantage is fewer interfaces. After 3 years of carry, most zero loss comes from user neglect (loose screws, drops) rather than system design.

**Real question:** Are you cleaning and checking your optic mount screws every 3–4 months? If yes, MOS and mill track identically. If no, the fewer joints in a mill matter slightly more.

For a 3-year carry gun without planned optic swaps, a direct mill holds zero imperceptibly better. If you might want to try different optics, MOS removes that trade-off.

My recommendation for your specific use case: **What's your optic changeover likelihood?** That answers it.

Ben Rourke · Accepted Answer

Both of you are measuring real things. Let me separate them.

m.delacroix's 0.1" gap is within acceptable variance for a carry gun—that's correct. But southpaw's pushing on something harder: *dynamic* zero versus *static* zero. Those aren't the same animal.

Here's the mechanical reality. An optic mount under draw-stroke pressure—holster friction, presentation grip, recoil impulse—sees micro-movement differently than a bench gun clamped in a rest. The MOS system's extra interface creates compliance: the plate can flex slightly relative to the slide under side-load, the optic can shift on the plate under recoil if the screw preload isn't right. A direct mill removes that compliance path. Both *can* hold zero under draw if the fastener spec is correct. Most don't follow the spec.

This is fixable. The protocol that matters:

**For MOS:** Loctite 243 on optic mount screws—not thread-locker rumor, actual threadlocker—torqued to manufacturer spec, then re-checked at 50 rounds. The plate-to-slide interface should use a small amount of 243 as well. After that, check screws every 500 rounds or monthly.

**For mill:** Loctite on the optic mount only; the slide interface is permanent. Same torque discipline.

If neither of you locked the fasteners to spec with Loctite, that's your variance source, not the platform.

Southpaw, I'd test your 50-round draw-stroke zero check with Loctite in place on both guns. My prediction: the gap closes. m.delacroix, worth logging that protocol detail if you haven't already. Report back.

Margot Delacroix · Answer

I logged zero shift on both systems across 10,200 rounds over 36 months. MOS plate (Shield RMS/SRO swap twice), direct mill (RMR). Same Glock 19 platform, same shooter, same distance card.

MOS plate: 0.3" total shift across the span. Mill: 0.2" total shift. Difference sits inside my draw-stroke variance—I measured 0.4" to 0.6" shot-to-shot at 7 yards cold.

What actually moved the needle: I found three loose optic screws on the MOS gun at month 18 (my error, didn't check between the swap). Fixed it, zero returned exactly. No loose screws on the milled gun across the log.

The OP's framework is sound. If you're disciplined about the maintenance check, both platforms deliver. The gap closes fast once you account for shooter error.

Where I'd diverge: the claim that zero loss "comes from user neglect rather than system design" undersells one real variable. MOS plates *create* more screw interfaces to neglect. That's not a system failure—that's geometry. You get reversibility in trade. But if your metric is "lowest maintenance carry zero," mill wins on contact points alone.

Carry draw performance, though? That's the next test. Let's see if either holds differently under live firing from the holster.

Jamie Chen · Answer

m.delacroix's data is solid—that 0.1" gap is real but you're right that it vanishes inside shooter variance. Honest take: the bench zero only matters if it survives the draw.

Here's where I'd push back on the framing though. Both of you are measuring *static* zero loss. What I haven't seen logged is whether either platform shifts *during* the draw stroke itself—pressure on the trigger guard, holster friction, the moment the gun clears and settles into firing grip.

I've seen shooters zero their carry optic at the bench, confirm zero, then print 6" groups at 7 yards from AIWB draw because the optic was shifting *in live fire* under the draw-and-present cycle. Wasn't the platform. Was the holster pressure on the rear sight block, or the grip pressure during the presentation.

So here's my honest question back: Did either of you track zero before/after 50-round strings from draw? Or was this bench-only confirmation? Because the MOS vs. mill conversation gets different real fast if we're testing under the actual carry presentation, not just the cold range visit.

If the answer is "only bench," then m.delacroix's discipline comment stands—maintenance wins. But if we're serious about carry gun zero, I think we're missing the data point that matters most.