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Discussion Starter · #1 ·
Pictured below is a Primary Arms Micro Dot (removable base model) mounted to a Midwest Industries offset mount. What's wrong with this picture?





Here's the sight mounted to a different rail, to rule out the rail.

 

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Sometimes when you buy Chinese made stuff you get Chinese tolerances.....
 

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It definitely does not. I'm surprised I didn't notice it sooner.
Sitting flush on the rail is not necessary, as long as it is stable and securely clamped down, i.e., does not move. I am more curious about what you mean by "does not hold zero".

That is a term normally used for scoped firearms where you shoot at varying magnification levels to verify it has the same impact point, or you make sight adjustments in each axis (as in a square box pattern), shoot a group at each adjustment point (corner of the square), and return to zero to ensure your zero impact point has not changed.

What is the typical spread and average impact point of your groups, both using the offset mount and the direct rail mount, and at what distance for each stated group? The handful of S2K's I've experienced were all capable of at least 2 inch patterns at 25 yards.

If you change the distance, the average impact point will change in the vertical direction on the direct rail mount, and along approximately a 45 degree diagonal line for the offset mount, if you are orienting the rifle at 45 degrees.

You also introduce a bit more flex and variability with the offset mount, but it should not be significant.
 

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Discussion Starter · #6 · (Edited)
I have had all sorts of problems with POI shifting with this optic, paying very close attention to maintaining a consistent rifle cant, at a fixed distance of just 25 yards. With the irons I can achieve 2" groups at that distance, but with the optic I can barely keep them all on a paper plate. I'm just wondering if this poor fitment has any part in that. I have several other types of red dot optics on other firearms, and none of them are crooked like this one.
 

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Sitting flush on the rail is not necessary, as long as it is stable and securely clamped down, i.e., does not move. I am more curious about what you mean by "does not hold zero".
Same here. I've got several optics that sit like that (or worse) but shoot to POA consistently.

I'd take that red dot off and shake it and see if it rattles. I think you got a bad egg!
 

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Discussion Starter · #9 · (Edited)
Same here. I've got several optics that sit like that (or worse) but shoot to POA consistently.

I'd take that red dot off and shake it and see if it rattles. I think you got a bad egg!
Really, because I have owned and own several optics, and none of them sit like that. Besides not engaging the rails as solidly, another issue I see with this is the elevation and windage adjustments won't be true vertical and horizontal.

When I first encountered the problem, I moved the sight over to an old Hi-Point, and it shot consistent POI. The rail on the Hi-Point is different though, it's not picatinny.
 

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Captains1911, what happens when you mount the optic directly to the rail that's on the weapon? How does that setup perform?

Do you have another weapon you can mount that red-dot to? That mount and dot combo to?

Let's systematically eliminate variables.
 

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Discussion Starter · #11 · (Edited)
Captains1911, what happens when you mount the optic directly to the rail that's on the weapon? How does that setup perform?

Do you have another weapon you can mount that red-dot to? That mount and dot combo to?

Let's systematically eliminate variables.
Yes and yes, as stated above. The third picture shows the optic mounted on a Daniel Defense AR-15 rail, and it sits in a similar fashion. I mounted the optic on another carbine and it shot consistent groups, but like I said, that firearm has a different type of rail. I don't have a mount tall enough to allow me to use the top factory rail on the Sub 2000.

I am confident that the M-Lok rail is attached securely to the handguard, and the offset mount to the M-Lok. I am suspicious of the handguard's rigidity, and so I removed it, installed an aftermarket stabilizer part that should make it more solid, and reinstalled the handguard ensuring all the screws are properly torqued. I have not had a chance to test out the rifle after this mod, but just noticed the sight "issue" and wondered if it may be the culprit.
 

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It looks like a jack-leg installation to me. I do not believe the plastic hand guard is a secure mounting point. Combined with the length of the total assembly I think the thing is shaking when fired and may be in a slightly different position with every shot. Seems to me you should have a simple 45 degree mount attached to the top rail. I guess you're trying to preserve the folding feature but it seems that you could do that a little simpler than the 'Rube Goldberg' contraption shown.
Prove it to yourself - grab the damn thing and wiggle it in all directions.
 

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Discussion Starter · #13 ·
It looks like a jack-leg installation to me. I do not believe the plastic hand guard is a secure mounting point. Combined with the length of the total assembly I think the thing is shaking when fired and may be in a slightly different position with every shot. Seems to me you should have a simple 45 degree mount attached to the top rail. I guess you're trying to preserve the folding feature but it seems that you could do that a little simpler than the 'Rube Goldberg' contraption shown.
Prove it to yourself - grab the damn thing and wiggle it in all directions.
The handguard is solid, especially now with the "Earley stabilizer" installed. The M-Lok is also a very solid platform. I don't quite understand how a 45-degree mount attached to the top of the handguard would be much different in terms of rigidity. Others have setups very similar to mine that they claim work, so I just need to figure out what the weak link is in my system, and the optic base connection seems glaringly suspicious.
 

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Yes and yes, as stated above. The third picture shows the optic mounted on a Daniel Defense AR-15 rail, and it sits in a similar fashion. I mounted the optic on another carbine and it shot consistent groups, but like I said, that firearm has a different type of rail. I don't have a mount tall enough to allow me to use the top factory rail on the Sub 2000.
Ah, gotcha. My apologies - I should have read more carefully your OP. :eek:

I am confident that the M-Lok rail is attached securely to the handguard, and the offset mount to the M-Lok. I am suspicious of the handguard's rigidity, and so I removed it, installed an aftermarket stabilizer part that should make it more solid, and reinstalled the handguard ensuring all the screws are properly torqued. I have not had a chance to test out the rifle after this mod, but just noticed the sight "issue" and wondered if it may be the culprit.
If the sight is holding zero despite the misalignment/mis-mating of the mounting surfaces on other weapons, then my suspicion would be that the handguard, regardless of current reinforement, is simply not up to the task.
 

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Discussion Starter · #15 ·
I sent the photos to Primary Arms and they confirmed that the base should not sit like that. They are shipping me a new base.
 

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When I first encountered the problem, I moved the sight over to an old Hi-Point, and it shot consistent POI. The rail on the Hi-Point is different though, it's not picatinny.
Heck, you got it, right there.

You moved the sight to another gun and the wandering zero disappeared. You replaced the sight on the problem weapon and the wandering zero reappeared. Check mount arrangement. As long as the picatinny claw is tight, the gap is meaningless.
 

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^ +1.

I'm hoping that the new base will fix it, but in all honesty Captains1911, in reading your posts, I would suspect the issue resides in where you chose to mount that particular sight and its mount, and that it is not related to the sight's base.
 

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Discussion Starter · #18 ·
^ +1.

I'm hoping that the new base will fix it, but in all honesty Captains1911, in reading your posts, I would suspect the issue resides in where you chose to mount that particular sight and its mount, and that it is not related to the sight's base.
Care to be more specific?
 

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^ Well, as Steve912 mentioned and as you've written before (as well as in reply to my confusion/request for clarification above, in posts number 10 and 11) you've ascertained that the sight itself, with that base, works on other firearms despite the obvious misalignment in the mating surfaces.

I understand that the misalignment is not as severe, but still.....

If the sight's base is able to firmly mate with the sight on one side and the offset mount on the other - despite the fact that it doesn't mate flush with its mounting surface on the latter - then it would stand to reason, to me, that either the offset mount's mating with its mounting rail on the weapon is problematic, or, in this specific case, that the handguard on which the rail mounted lacks the necessary rigidity to serve the purpose of being a place to mount an optic/sight.
 

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Discussion Starter · #20 ·
I'll report back once I get the new base for the optic, and have a chance to go test it out.
 
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