Pistol Optic Mounting Problems and Solutions Thread

[Clusterfrack]

This thread is for cataloging and discussing common (and not-so-common) issues with mounting optics on handguns, and how to solve them.

Hopefully as RDS mounting technology matures, this thread will become irrelevant. Unfortunately, that may take some time.

[GJM]

Screw VC3!

Buy Fix it Sticks

[Clusterfrack]

Ok. Here's the weird issue that inspired this thread. I had a CZ P-07 slide milled for a Holosun EPS at StoneBridge Gunworks. SBGW has done excellent milling for me, and I continue to recommend them. Every one of their milling jobs for me has been very precise, and the optics required only a few clicks to zero. This job was no exception.

The Problem: The gun shot a tight group--except for random fliers high right, and high left. These were fairly big deviations: >6" at 15yds.

@JCN suggested that I measure the screws and make sure they weren't bottoming out. I thought that was unlikely because the optic was very tight in the pocket, and could not be moved by hand. Turns out he was right.

The machinist apparently drilled holes that were exactly the length of the screws, and bottomed out at 15 in-lbs. The tightness of the milling job kept the optic in place for most shots, but somehow it moved enough to throw fliers.

The Solution: I ground down the screws by 1 thread, bedded the optic with E6000 glue, applied blue Locktite to the screws, and tightened to 15 in-lbs. Tight group. No more fliers.

From now on, I will be either having slides milled and mounting the optic myself or checking mounting.

[sickeness]

Can someone please help me mount a 509T on an M&P CORE in a way that doesn't involve having to use a garbage, out of spec C&H plate?

[MickAK]

Ok. Here's the weird issue that inspired this thread. I had a CZ P-07 slide milled for a Holosun EPS at StoneBridge Gunworks. SBGW has done excellent milling for me, and I continue to recommend them. Every one of their milling jobs for me has been very precise, and the optics required only a few clicks to zero. This job was no exception.

The Problem: The gun shot a tight group--except for random fliers high right, and high left. These were fairly big deviations: >6" at 15yds.

@JCN suggested that I measure the screws and make sure they weren't bottoming out. I thought that was unlikely because the optic was very tight in the pocket, and could not be moved by hand. Turns out he was right.

The machinist apparently drilled holes that were exactly the length of the screws, and bottomed out at 15 in-lbs. The tightness of the milling job kept the optic in place for most shots, but somehow it moved enough to throw fliers.

How often did it throw fliers? Did it return to zero after each flier? Can you see any material ground off from the optic occasionally shifting?

That's an interesting problem.

[GJM]

A common issue is a screw being too long and causing reliability in Glock pistols, as it presses on the bearing rod/spring. It is why I confirm reliability, as well as zero, post an optic installation.

[Clusterfrack]

How often did it throw fliers? Did it return to zero after each flier? Can you see any material ground off from the optic occasionally shifting?

That's an interesting problem.

Interesting is a good way to describe it…

It returned to zero every time over about 150 rounds. It was baffling.

There was no visible damage to the optic or the slide mounting area. I think it was a purely elastic deformation resulting from compression of the optic screw pockets and stretching of the screws. Possibly, the optic moved slightly and stuck until the slide cycled and it returned to “neutral”. Pure speculation…

I’m just glad this solved it, rather than the issue being with the optic or the gun.

[JCN]

Interesting is a good way to describe it…

It returned to zero every time over about 150 rounds. It was baffling.

There was no visible damage to the optic or the slide mounting area. I think it was a purely elastic deformation resulting from compression of the optic screw pockets and stretching of the screws. Possibly, the optic moved slightly and stuck until the slide cycled and it returned to “neutral”. Pure speculation…

I’m just glad this solved it, rather than the issue being with the optic or the gun.

My leading hypothesis that lead me to suggest this as the culprit was that if the screws weren’t fully mated down, then the optic could rotate (one touching front of screw, the other back of screw).

So basically you have three positions the optic can be in. Centered forward or centered rear. Rotated to the right or rotated to the left.

Remember how some people noticed that Holosuns are angled to the right when mounting… if they don’t hold the optic in place while they torque…same thing. It’s a variation of making sure you mount scope rings pre-pushed evenly against the front edge of the rail slot rather than floating in the middle of the slot.

But a handgun has a snap back and a snap forward. So that’s why the return to zero with fliers smelled like loose mounting despite it not looking or feeling like it at the time.

[JCL]

Do handgun optics have something analogous to a bore axis that would allow computation of the displacement required to move the POI 6” at 15 yards?

[Clusterfrack]

Do handgun optics have something analogous to a bore axis that would allow computation of the displacement required to move the POI 6” at 15 yards?

6” at 15yds = 40moa = 11.6mrad = 0.66deg.