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How to Mount your Optic (Optic Ready Slides ONLY)

Optic ready pistols come with the cover plate pre-installed and torqued at the factory.  We use medium strength blue Locktite on the screws, but they can be removed with hand pressure and a typical hand tool.

Screws require a torx T-10 driver and should be torqued to approximately 10 inch pounds.  If you do not have a torque wrench and are using a typical hand tool, most people describe this as “very snug, but not excessively tight.”

Medium strength blue Locktite is recommended for mounting screws but is optional.  If you choose not to use Locktite, we recommend re-torquing screws periodically and after every range session.  Loose screws can cause zero shift.  If many rounds are fired with the optic loose, thread damage could result.

Your pistol will come with a total of 5 screws.  THE SCREWS ARE DIFFERENT SIZES.  Please note the following:

  1. Cover Plate Mounting: Use 2x 1/4 inch long screws.
  2. Trijicon RMR Mounting:
    1. 1x 5/16 inch long screw goes on the EJECTION PORT SIDE
    2. 1x 3/8 inch long screw goes on the NON-EJECTION PORT SIDE (we add the 3/8 inch screw to maximize the strength of the mount as there is space for it when mounting the RMR. However, a 5/16 screw will also provide adequate strength).
  3. Holosun 507c Mounting
    1. Use 2x 5/16 inch screws.

Call us if you need replacement screws.

69 Replies to “How to Mount your Optic (Optic Ready Slides ONLY)”

  1. Alex Beckworth says:

    I’m trying to mount a plate for a vortex venom on my Kimber KHX Custom, and the stock screws that hold the stock sight plate are too tall to fit under the venom sight. Will your countersunk 1/4” screws thread into my Kimber slide?


      Hi Alex, I wish we could help but we don’t know the thread specifications for the Kimber.

  2. Marlin Begalke says:

    Will vortex or holosun optic fit right in the 918, the dimensions seem the same but I’m unsure and want to know more before buying the optic.


      The MR918 can fit an RMR or SRO from Trijicon and a 507c or 508t from Holosun. Unfortunately, the Vortex does not fit the MR918. However, the MR920 will accommodate the Vortex and other brands.

      1. Julien boudreault says:

        Hi i have a vortex sight. Do you have a solution to fit on the mr918 ?


        Hello, unfortunately the Vortex sights do not fit on the optic cut on the MR918. The new optic c ut on the MR920 was created to solve for this and does fit the Vortex Viper.

      3. Matthew Lee says:

        This is not an accurate response. I have an MR920 and purchased a Vortex Venom red dot, the mounting holes do not align correctly.

      4. Jessica Roe says:

        Hi Matthew, the Vortex Venom does not fit. The Vortex Viper does fit the MR920. You can find an updated list of optics that we have tested here: https://shadowsystemscorp.com/mr920-how-to-mount-your-optic-optic-ready-slides-only/

  3. Trung says:

    Will I require a sealing plate with my RMR?


      Yes, you’ll likely want to use one. Without the sealing plate water, oil and debris can get under there.

  4. Patrick H Morgan says:

    Was wondering if I needed sealing plate for attaching
    a holosun507c to my mr920 elite. If so what would you recommend?


      Hi, you do not need a sealing plate for Holosun, as their case is fully enclosed. We do recommend one for the Trijicon RMR, as its case is not fully sealed.

  5. John says:

    Good evening, I have a shadow slide and mounting a 507c to a factory RMR cut. The 5/16 4-40 recess mount screws don’t hold the sight in place. It rattles in the cut.

    1. Jessica Roe says:

      Hello John!
      It sounds like the slide you currently have had the old optic cut on it. It’s an earlier vintage than the Holosun 507. Don’t worry though!  The easiest way we have found to get things secured is to use a type 2 RMR sealing plate.

      This sealing plate acts as a shim right raise the housing up. Unfortunately the dimensions of the housings of the RMR and 507c are not identical.

      If you need any further assistance or clarification, please feel free to call or text our Technical Manager Richie at 469-343-6831. He will be ready to take your call.

  6. Jonathan says:

    I’m trying to mount a Vortex Venom on my MR980 Elite and finding that when the screws are lined up the back of the optic will not seat in the cut, about a 1/32inch overhang. Do you have any solutions or should I get a different optic?

    1. Jessica Roe says:

      Hi Jonathan, Unfortunately,the Venom is too long to fit the optic cut. The Vortex Viper does fit and has been tested to work great with the MR920.

      1. James Morgan says:

        Just to be clear, your saying the Vortex Viper fits a MR918 optic cut?

      2. Jessica Roe says:

        No, James, sorry for any confusion! The MR918 optic cut can only accommodate RMR-footprint optics such as the Trijicon RMR and SRO or the Holosun 507c or 508t. The newer MR920 (released in January 2020) has a new optic cut that allows a multi-footprint mounting system to accommodate most major optics (including the Vortex Viper) with a direct mount to the slide–no intervening plates or adapters needed.

  7. Jakob byars says:

    I have the ss9c and I need the 5/16 screws like 10 and I’ve tried calling like it says to but I can’t get ahold of anyone I can even pay for them but they strip quick and I need to get my 508t on

    1. Jessica Roe says:

      Hi Jakob, Our offices were closed for the July 4th holiday weekend, which is why you didn’t get an answer to your phone call. Here is the link to purchase additional screws for the old-style optic mount: https://shadowsystemscorp.com/product/mounting-screws-old-generation-rmr-optic-cut/

  8. Jay says:

    Hello lads.

    I have one of your slides for a G19 with an RMR cut, however, the holes are tapped in what appear to be 4-40, while the RMR07 I acquired came with 6-32 screws.

    Now what?

    1. Jessica Roe says:

      Jay, please email me your address to jessica@shadowsystemscorp.com. I will get some screws out to you!

  9. Joseph Newing says:

    Will the MR918 fit the sig romeo red dots?

    1. Jessica Roe says:

      No. The Sig Romeo Pro 1 does fit the MR920, but not the MR918.

      1. Ronald Adkins says:

        The Romeo 1 has the same footprint as the 1 Pro, but the manual says to use screw 3 on the 920 (long screw). That would leave the screw protruding above the device, which I’m sure is not the intent. Is that accurate?

      2. Jessica Roe says:

        Ronald, Thank you for highlighting this typo with the chart! You are correct–the Romeo 1 Pro requires the #1 screws.

        We have not tested the non-pro version of the Romeo 1–despite the footprints being “the same,” that is really only a 2-dimensional measurement. To ensure fitment, our team will need to test the optic. In the meantime, I have confirmed with SIG that the two optics do not share the same 3D measurements and thus we cannot say whether or not that optic will fit until our team tests it.

  10. Matt Dahlgren says:

    Is the holosun 507c supposed to be a “press fit” with your SS9c slide? It won’t sit down over top of the posts.

    1. Jessica Roe says:

      Hey sorry it took me a while to get back to you on this. I had to check with my engineering team. The Holosun should not be a press fit. If your slide is early enough vintage, it is possible that the bosses are too big for a Holosun. We designed the system before the Holosun came around and made a few changes after it entered the market to improve fit. If an RMR fits, that would explain it. However, do you have access to calipers for measuring (many shooters seem to have them due to reloading, etc.). If so, let us know what the post diameter is and we can confirm all this. Let us know your thoughts. Please feel free to email me directly at jessica@shadowsystemscorp.com

  11. braden chamness says:

    I have the romeo zero red dot for the canik tp9 sc. I lost my sealing plate that came with my firearm, and I cannot seem to find a replacement anywhere online or in store. If you know where I could get a sealing plate for the canik tp9 sc please let me know because I cannot use the red dot without it. thank you

    1. Jessica Roe says:

      Braden, we do not make parts for Canik pistols. You may want to try their website or go directly through SIG about the optic. Good luck

  12. Jonathan Ponder says:

    I recently purchased the MR918 slide with the RMR cut to accommodate my Holosun 507c. Which screws am I to use? The two sets of screw that came with my red dot are to big and will not thread into the slide.

    1. Jessica Roe says:

      You’ll want 2 of the 5/16ths length screws. They can be found here.

  13. Jared says:

    I have a MR920 elite and a Burris Fast fire 3 red dot does not like up with the holes on the slide (too far forward and it hits the front of the rear sight dove tail before the holes line up). I’ve machined the holes out on the red dot to allow them to fit but this isn’t what I expected.

    1. Jessica Roe says:

      Hi Jared,

      The Burris Fastfire does not fit the MR920. There is a full list of optics we have tested listed in our FAQ.

  14. Pstew says:

    Will the Swampfox Liberty fit the MR920?

    1. Jessica Roe says:

      Yes, the liberty fits, using Spacer A and Screws 1.

  15. John says:

    I have a MR918 for a Gen 4 G19 and recently purchased a Holosun 509T. The Holosun comes with an RMR plate and says it will line up with an RMR cut slide. The holes appear to line up but the Holosun plate will not drop on to the MR918 slide posts and the screws provided by Holosun are to large for the slide threads. Any solutions to make the 509 work with this slide?

    1. Jessica Roe says:

      Unfortunately, the 509T will not mount on the MR918.

      1. Don Gregory says:

        will the 509t work on the mr920?

      2. Jessica Roe says:


        The 509t can SOMETIMES be mounted using the cover plate screws. The “sometimes” comes from variances we have seen in how the Holosun screw holes are chamfered–sometime the cover plate screws do not seat well enough for a secure mount. We are working on new screws for that optic.

  16. Nobody says:

    Do any of the optic options mentioned Co witness with the mr920?

    1. Jessica Roe says:

      Hi, You will get a generous lower 1/3 co-witness with all approved optics except for the Deltapoint Pro. The DPP optic body is too high for any co-witness, even with suppressor height sights.

  17. Michael says:

    Hi, I’m trying to mount a Holosun 507K to a S&W M&P 2.0. Canyou tell me what mounting plate I need and do you sell those. Thanks.

    1. Jessica Roe says:

      Hi, I’m sorry we do not have advice for mounting that optic on a S&W product. You may want to reach out to Holosun or Smith & Wesson customer service.

  18. Anthony says:

    Good day,
    I bought a Shadow Systems MR918 Elite slide. It’s a great slide by the way. When I mounted my Holosun 507c-GR optic onto it, the screws supplied were too wide in diameter to screw into the posts on the slide and thus I am unable to secure the optic to the slide. Any help would be most appreciated.

    1. Jessica Roe says:

      The screws that come with the Holosun are too big to fit the MR918 slide. You will need to use the screws supplied with the slide. Spares can be ordered from our website. Mounting Screws: Old Generation RMR Optic Cut

  19. Ken says:

    Hello, just confirming that if I mount a Holosun 507c on my MR918L that I will be able to co-witness with the original factory sights.

    1. Jessica Roe says:

      Yes, you should get a generous lower 1/3 cowitness with that sight in our optic cut.

      1. Ken says:

        Thank you. I appreciate the update.

  20. Steven Stark says:

    Need longer screws to mount my 507K to a kimber R7 mako with the C&H Precision Weapons plate,the screws arnt long enough to snug down sight

    1. Jessica Roe says:

      I’m sorry, but none of those are our products.

  21. Jesse Pollock says:

    Just picked up a DR 920 and would like to mount holosun 509t. Will this fit on the gun and if so what size screws should I use?

    Thank you.

    1. Jessica Roe says:

      Hi Jesse,

      The Holosun 509T is mostly compatible with our optic cut. It can usually be mounted using the Holosun adapter plate included with the 509T, our “A” spacer, and our cover plate screws. The screws will sometimes sit slightly proud of the adapter plate, and so they may contact the underside of the optic. This will cause superficial wear with regular use.

      In some rare cases, due to manufacturing variances in the Holosun adapter plate, the adapter plate and cover plate screw combination may not provide sufficient clearance to allow the 509T to mount. I hope this information is useful for you. Let me know if you have any other questions!

  22. Masi Z says:

    I purchased the MR920L Elite and i noticed that on the slide it only has 2 mounting screw points or an optic? Unfortunately i cannot fit a Holosun HS507k as the pitch on the holes is off. Is there a difference as i see some slides come with a offset of 4 mounting points on the slide.

    1. Jessica Roe says:

      Masi, if you have an MR920, there should be four screw holes. Is it possible you have an older MR918? That model had a mounting cut for an RMR footprint. If you’re unsure, please email us some photos of what you’re seeing? Support@shadowsystemscorp.com

  23. Ignacio says:

    Will the Crimson Trace “CT RAD MICRO PRO (GREEN)” or “CT RAD™ PRO (GREEN)” fit the MR920 Elite?

    1. Jessica Roe says:

      We have not tested them.

  24. Jon says:

    Hey Jessica, will the hs407k fit on my mr918 elite? Thanks

    1. Jessica Roe says:

      No, it will not fit the MR918’s optic cut.

      1. Jon says:

        Thanks, are you able to give me a list of Holosun red dots that are compatible? Or one that’s most recommended? (For mr918)

      2. Jessica Roe says:

        The MR918 can fit the Holosun 507c.

  25. Lenny Schwartz says:

    I have an XR920 and bought a Trijicon RMRcc. The screw holes do not line up. Is there a particalar Trijicon model that works with the XR920. I see lots of post using this sight on the MR 920 but not the XR

    1. Jessica Roe says:

      The RMRcc does not fit on our optic cut. The Trijicon RMR and SRO will fit, as will any of the optics listed in the chart on this page.

  26. Than McCracken says:

    Do I need a base plate to mount a Trijicon RMRcc to a Kimber R7 Mako (Optic Ready)? If yes, what base plate do I need? Thanks

    1. Jessica Roe says:

      Hi Than, we do not make Kimber pistols and are therefore unfamiliar with their optic cut. You’ll need to ask Kimber instead. Good luck!

  27. Michael Eason says:

    One of my CR920 plate screws came out without issue but the 2nd screw stripped almost immediately. Do you have a suggested extraction bit size that I should try or should I create a ticket to send the slide in?

    1. Jessica Roe says:

      Michael, please email my Technical Team at support@shadowsystemscorp.com

  28. Larry Land says:

    What is the thread pitch of the rmr mounting holes? I bought a new Swampfox Liberty. The #2 screws that came with the 920 will screw it down but their head is large and covers the edges of the battery compartment and I can’t remove the battery without unmounting the optic. The screws that came with the Swapfox do not have the correct thread pitch to go into the holes on the side. I need screws with a smaller head and the correct thread pitch. If you can tell me what the pitch is, I can contact swampfox to see if they have them.

  29. Joe F says:

    Optic plate screws stripped (well, one came out once, but then stripped the second time I tried to remove it).
    Optic screws were INSANELY tight…I watched the recent video about holosuns and the CR920, AND used the “circle NO PLUS SIGN” spacer for an EPS Carry (which seemed as tight or tighter than the + one), as well as the flush screws.
    Holy crap.
    One went in all the way, but bent my T10 torx head (I was having to put vice grips on the torx bit to get it to turn)…the other one stopped like 1/4mm short of flush but seems to have been stripped or something (it was tight even without the sight on, but I thought maybe it just had some loctite on it or the holes were just super tight).

    I’ve now spent $30 ordering the best T10 torx bits I can find as well as different T10 drivers to see if I can tighten and loosen these screws. Also ordering new screws on SS’s website. I need a new optic plate since mine got scratched up bad extracting the stripped screw, but I don’t want to pay that much–sure wish there was a cheaper polymer option.

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