Glock 20 MOS with Trijicon RMR co-witness Q&A

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Sep 26, 2010
Hey guys,
It has been quite some time since I have posted on this forum. I am now coming back for a little help!

I finally got my hands on a Glock 20 MOS at a reasonable price! I now have plans to put a reflex sight on top with possible suppressor sights. I plan on purchasing Trijicon for both. I purposely bought this handgun because A. it's super cool, and B. I plan to hunt with it.

With hunting in mind, I would like to go with the 3.25 MOA version of the RMR to make 75-100 yard shots.

My main question... Is the RMR a direct co-witness with the suppressor sights? Does the red dot sit directly on top/in line of the front sight? Or is it above the sight?

Thanks in advance for any help!
I don't have the Glock MOS but I have the M&P9 version that is similar and an FNP-45. Both wear the tall "suppressor" sights. The "co-witness" with the irons is at the very bottom of the window as the sights, tall as they are, are only about 1/8" above the bottom of RMR window

Unless your suppressor sights are adjustable you are unlikely to get the exact co-witness sight picture you might like.

OTOH if your irons are dead-on, you can adjust the RMR dot to sit however you like with respect to the sight picture with the irons. Meaning if your POA/POI is "perfect at the distance you want with your irons, you can adjust the RMR to put the dot on the irons however you like for that POA/POI.

The problem with iron sights and red dot co-witness is that you need to use them very differently -- with the irons you focus on the front sight, with the red dots you focus on the target and look "through" the dot. If you focus your vision on the dot as if it were an iron sight or a reticle, you'll swear the thing "does not hold zero".

These two guns came with the suppressor sights, I got them to mount an RMR, I'd never pay to have taller sights added to a pistol with a red dot unless you are expecting battery issues and want a backup. I go with the RMR "dual illuminated" sights -- no batteries.
Yeah so I just checked glocks site thier is no glock 20 mos so no you don't have one as to what you have I have no clue maybe you can clear that up for me
40MOS? seems like Glock likes to screw everyone up with their numbering schemes.

I have a MOS with DP Pro but do not run co-witnessed sights.
My experience with RMRs is they typically don't exactly line up, even with suppressor or "cowitness" height sights. Plus, the experience of shooting a dot is very different from shooting irons. With irons you focus hard on the front sight (or you're supposed to) and with dots you basically focus on the target. IME it's better to EITHER use the irons OR the dot, but not try to use both at once.

I'd sight in the dot holding it center of the window, and ignore the irons (unless your dot goes away).
Because of the "universal" mounting system of the Glock 40 (10MM w/MOS)
it's not really practical to have co-witnessed irons.
(Unless you wanted to have uber-custom towering beyond-suppressor height irons).

I looked at the G40, and decided to go with a G20 with a slide milled for Trijicon RM07 and suppressor sights for co-witness. So you have to pick a single model of an RDS for the milling job and stick with it.
Awesome insight guys! Thank you! I think I got my answer.

Yes, it's a Glock 40. That was my sliding a post in right at the end of my lunch break.

I guess I should clarify. I DONT want the sight and red dot to co-witness. I'd prefer the dot be above the irons and the irons visible in the lower window. I do want irons as a back up.

Thanks again!
IME, There are no sights high enough to be used with the optic installed, period. To use the regular sights the optic will need to be removed from the slide.
Thanks guys. This has been a big help! I might just go look check the RMRs out at my local gun shop before purchasing.

I agree that it look like Glock didn't think through the co-witnessing properly. But it looks like it is going to do exactly what I need it too. I did a bunch of google imaging searching last night, and though there are not many photos, everything you guys are saying lines up. The Trijicon suppressor sights look like they are barely visible through the window.

Nice pic agtman!
I agree that it look like Glock didn't think through the co-witnessing properly.

Id disagree.. The sight doesnt need to be co-witnessed at all... A RDS on a moving slide is something you have to commit to 100%, to get it right.. Cluttering up your sight picture will not help that..
Cowitness just means you can see the dot and the sights through the same window. Most people want the irons either folded (on a rifle) or in the lower 1/3 of the optic window to keep them out of the way.

On a pistol, sorry, this is ridiculous. Pick one and stick with it. The little window on the micro dots would be way too cluttered with sights in it as well, at least in my opinion.
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