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.

[JCL]

6” at 15yds = 40moa = 11.6mrad = 0.66deg.
I’d like to know how much the optic needs to move in order to produce that much of a shift.

[Clusterfrack]

I’d like to know how much the optic needs to move in order to produce that much of a shift.

A little under a degree of angle? But I see what you’re getting at, and not sure.

[JCN]

I’d like to know how much the optic needs to move in order to produce that much of a shift.


A little under a degree of angle? But I see what you’re getting at, and not sure.

In most mounting there’s ability to rotate it one degree.

The Shield RMS are worse because they don’t have center locating angled heads. The caps sit on top of the optic and you can shift many degrees.

It’s one of the reasons I generally space fill bosses to remove that ability.

This is a typical plate E6000 application for me. Dab on bosses and very light smear on body.

98680

[JCS]

I recently encountered my first stripped screw removing an SRO. That was fun... Not. I don't have a drill press so I ended up using a hammer and a Torx bit and driving the Torx bit into the softer metal of the screw to get it loose.

[JCS]

Also I found it surprising that Dave Dawson recommended red loctite for installation on a Staccato.

[JCL]

…In most mounting there’s ability to rotate it one degree….

Interesting, I thought that it was a closer interference fit. That would certainly allow for the issues Clusterfrack was experiencing. I had a screw length issue manifest with ejector plunger interference on a Glock slide. It’s a small sample size, but the number of issues Clusterfrack and I have encountered leads me to believe that demand for slide milling services currently outstrips top quality supply.

[Clusterfrack]

JCL, I can’t argue with that conclusion. I dislike relying on gunsmiths in general because few treat their work as life safety equipment.

I still think direct milling is less prone to issues than factory plates. But, I’m going to be doing my own mounting, or checking work carefully.

[JCN]

Interesting, I thought that it was a closer interference fit. That would certainly allow for the issues Clusterfrack was experiencing. I had a screw length issue manifest with ejector plunger interference on a Glock slide. It’s a small sample size, but the number of issues Clusterfrack and I have encountered leads me to believe that demand for slide milling services currently outstrips top quality supply.

With mounting screws that sit fully on top of the optic (like RMS), the bosses are what keep the optic from rotating (which is why I use E6000). The nature of threaded screws in optic holes allows for wobble and slop.

Which is why the post screws with snug locating caps on the DPP are great. They take up some of the room in the optic screw hole and more positively anchor the optic from rotating.

With a “flat head” screw mount that has a tapered cap underside, if it’s a little loose because it’s bottomed out then it has ability to rotate and shift a little. One degree is a tiny amount visually when looking at it from the outside. But that wiggle and wobble allows for multiple positions of the optic.

I was joking with Clusterfrack because I know all this because I have moved optics around to a lot of different guns, plates and platforms over the years. So I’ve screwed a few things up and now pay close attention to screw lengths.

[JCN]

JCL
Clusterfrack

If it helps visualization, do the following experiment either in your head or on a spare optic cut….

Put a long screw into a hole… only secured by 3 threads. How easy is it to wobble the screw with the long torque arm of the long screw. Take your fingers and scissor two of those and if you can get one to wobble 1/2 a mm forward and the other 1/2 mm rearward in the other direction… there’s your total 1 degree of rotation.

The tension on the screw pulling down on the optic body is what prevents this and also space fills. With screw bottomed out there’s not much tension on the optic and you get some micro wiggle.

It’s another reason why I try and do a little grip augmentation of the optic on the plate with E6000.

[JCN]

The most common too long screw issue is when someone uses a too long optic screw on a plate that’s open underneath. It ratchets up the plate and stresses the mounting screws of plate resulting in a number of failure modes. Sheared screws, loose screws, inconsistent zero, out of adjustment ability, etc.

[Tannhauser]

Good thread. I’m following for tips.

I first read about E6000 on this forum, and now it’s part of every optic installation I do, pistol or rifle.

I mounted Picatinny rails on a couple of inline muzzleloaders this year. One fir me and one fir a friend. I was generous with the E6000 under the bases. Maybe too generous. But both have been rock solid.

Just curious why the dislike for VC3?