I will call this round #2 of test since last Friday the Thermal was sighted in.
So went to same range same setup and fired 3 rounds to check if zero was solid after a weekend of bouncing around being turned on off a bunch and recharged.
Here is 3 shot group at 100yds
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So far so good!

Ok round number 3

Rifle scope ammo kind of cold as left in truck last night.
First shot was a little higher so maybe cold bore then dropped back down to normal zero just slightly right

That would bother me on a known great shooting rifle and load.

So round 4 is on paper.

I’ve had no issues with my FLIR PTS536 losing zero. It’s been mounted on the same rifle for more than 4 years and used extensively with no loss of zero. Yesterday I was sighting in a lever action and needed to fire a few rounds to train the video recording feature again. After doing so, I had 6 rounds left and shot my 100 yard steel target. Here’s the results.

I have limited experience sighting in thermals, but I did just do it on one of the new Pulsar Talion's, and it was definitely tricky. I don't see you mentioning which Thermion you have, but depending on how good your resolution is at 100 yards it might not necessarily be that your gun is off. Perhaps it's having difficulty picking up a hand warmer size heat signature at that distance. I certainly felt that was a little tricky at 100 yards in the Talion. It sort of fluctuated a square pixel up and down. I'd be curious if you tried to zero closer than 100 for sake of testing and see if you get similar issues and/or does it improve the heat signature at all.

A 50 yard zero with standard cartridges ends up also being about a 200 yard zero as well. Unless you’re shooting a lot further at night than I am, I wouldn’t bother with anything more complicated. Just a thought …

I sighted my Pulsar in 2 weeks ago on my 300 blk out AR-15. The barrel is a match barrel, and will easily hold sub moa, often putting several bullets in a tiny cluster. When I sighted it in, it was 3/4" to the right. I checked it again last weekend, and it was exactly 1" low of center, both at 100 yards. The first 2 shots went into the same hole at 100. I sometimes see a slight POI shift, which is frustrating.

The reticle on a thermal is like the mouse pointer on your computer. Counts pixels to set the point. Doesn't take much to get it off by a few. It's not so much a temperature problem as a design problem. Noisy circuits make for lousy accuracy, electronics wise.

My old Thermion XG50 kept losing zero after 2 years of owning it.

I did some software updates but that didnt fix it.

Had to send it in, they replaced the scope.

Good discussion.

Sounds like it's not an optical system at all but more like a video camera that can only paint the reticle through digital circuitry?

LOL, that is one way of looking at it, but you are correct, there are not actual/physical crosshair, not on thermal or most electronic optics. You won't find physical crosshairs on the guns targeting system of a F16 either. The reticle is done on a display that could be said that it looks like a video game.

The thing is, the thermal reticles don't move around when you are shooting. You can't move them so far to one side that you break the mechanism inside. There is no systemic thermal optic reason reticles are purporting moving willy nilly. If this was a real problem across thermal optics as implied by the OP's example of a dozen or so scopes, people would be complaining all the time.

So if there is a change in magnification or zoom, the thickness of the reticle must change using more or fewer pixels to keep the appearance the same? With optical systems not being tied to the placement and size of video pixels, it would seem sight accuracy could be compromised. I mean, at certain distances, what's to keep the actual aim point to fall somewhere between pixel lines.

These scopes aren't being used for a 1000 yard Camp Perry National Match. They are being use primarily to shoot at critters inside 100 yards for most people, 200 yards for a lot less people, still less for 300, and even less at 400 yards.

The error that you are talking about is going to be a fraction of a pixel. On scopes that zoom 2x, 4x, 8x, that fraction will be 0.5. The scope doesn't use half pixels and will place it on one side or the other and you will be a half pixel off at most. That amount is small enough to not be noticed by most shooters as it likely falls within the usual group size of the ammo, environmentals, etc.

This is not anything remotely resembling what the OP is talking about with wandering points of impact where multiple shots will be in one place and then all of a sudden, a shot will be a flier.

I'd like to know more about the electronics and digital processing in these things.. I've been in the field for 46 years and have worked with a lot of pretty high tech stuff over the years, and how they're thought out and designed can be pretty damned interesting.

With many digital devices, what the casual user thinks is happening often bears no resemblance whatsoever to what is actually going on in a device. The stories I could tell, that no one would see the point...

Ones and zeroes are amazing.

Anyone have any Trijicon thermals? any issues with NOT holding zero?

I have hunted with them for years now and have the IR Hunter 4.5x 60mm. Properly mounted with reliable ammo and a good shooter and it holds zero just fine. You can literally see years of me using the same scope on YouTube in hundreds of videos.

Don’t you find the 4.5x field of view very limiting?

Yes, they work just like my 30 yr old Sony camcorder, scan the CCD sensor, and pass data on to the LED screen. NV doesn't use the daylight filter camcorders do (my sony the filter is removable). IR uses Vox sensor and germanium glass that passes IR. Reticle is superimposed on the OLED screen (lower power than LED). Raster position is saved in nvram. Any noise in the raster sync will cause jitter or error. Should be corrected by restart of the scope. If not, return it. Got nice 3 shot group with the Rattler on BO pistol @ 50 but didn't get zero right. Try again.

I don't have a rifle scope for viewing so FOV isn't nearly as critical as I don't use the rifle as my scanner to find targets all night long. I have a rifle scope for shooting. I have a handheld spotter for viewing and it is a Trijicon IR Patrol 4.5x 60mm. Do I find it limited for viewing? Sure, but then I just turn my head and I can see all that I need to see, but with more magnification. Comparatively speaking, I spend very little time behind my rifle scope and a LOT of time behind my spotter.

It works for me. More magnification or less, each way has advantages and disadvantages. You just have to figure out what works for you.

Is there is any simple way to test for this? Perhaps something as simple as putting the rifle in a vise, pointing it at a target, and then periodically checking to see of the reticle position has changed?

No

Your human eye can see it happen

You need a special piece of diagnostic hardware and a trained technician to know what is going on

Or just sell the scope and try another (easy method)

I have spent more than 10K for about 4-5 thermal and NV scopes. I have ATN and PARD. I would like to share my experience with people. All of my digital scopes have zero loss problems. I don’t trust the digital scopes now. What you can do is to get a NV clip on scope to mount it on your regular optics scopes eyepiece. In this way, you use your normal optics scope reticle to aim your target. This is the only way I trust for now.

There should be some good digital scopes, but definitely not below 5K or 8K. The products we spend 2-3K to get are all toys, not the real thing. Don’t waste your money to try. Otherwise, you spend big money to get a military grade .

Maybe SIG SAUER or BURRIS make good digital scopes. I never tried, and don’t dare to spend more money to try. I guess the manufacturers who make optics scopes should have better idea how to make trustable digital scopes.

In fact, you only use thermal or NV to shoot hogs within 100 yard, or maximum 200 yard distance. A NV clip on scope is fine for such applications.

Actually put the Rattler on my BO carbine, bore sighted OK. Removed it and replaced it, one shot to verify boresight- right on. It's a 384 resolution that is >1" @ 100 by specs. Therefore, by the specs you can't get better than 2" accuracy @100. POI COULD be repeatable to POA. So the OP scope is actually OK.