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Posted: 4/28/2021 10:15:08 AM EDT
[Last Edit: 4/28/2021 1:00:58 PM EDT by SilasB]
I mount optics on P365s and P320s regularly. Do a lot of Sig business, certified armorer in both platforms, etc.. Decided to write something down after reading yet another 'stripped screw' thread.  If you have corrections, alternate methods, tips, please post.

P365 XL


Firearm does not need to be disassembled for installation. Lock the slide to the rear, invert pistol to access the two mounting screws. Alternately, remove the slide. Task is easier if you secure the firearm/slide. I use a vice with soft jaws.

There is no thread locker on these screws.

I use a H5222X bit to remove the screws. With the firearm/slide secured, steady, smooth pressure and both screws come out with ease.  Don't hold your tool at an angle, don't imitate an impact wrench, etc.

Why not use Allen or Hex keys? Short answer - they're too sloppy. The fit is looser than you realize. This means your tool will turn within the drive section and strip the screw.  

The H5222X bit edges are much sharper providing a tight fit. If the bit starts to show wear, I toss it. I buy them in packs of five. You can purchase individual bits from Granger, other supply houses, and even from our benevolent overlords, Brownells.

As far as mounting your preferred optic. Follow the recommended torque spec. If you don't have the proper tools, finger tight + a quarter turn won't mess anything up.

RomeoZero Red Dot

Do NOT adjust the elevation or windage turrets while the optic is off the gun. Additionally, when adjusting for zero and the turret stops moving, you have reached the end of adjustment travel for that turret. Turn beyond that and you will need a new red dot. If stop points are reached and you are unable zero red dot, contact Sig Sauer.

Do use the supplied clear plastic shield piece when mounting the optic, sticky side to the slide not the bottom of the optic.

If the shroud was included with your RomeoZero purchase, do install it. RXZs can be retrofitted w/ the shroud. Believe Sig is charging $25 or so for this currently.

Make sure to use the P365 screws and not the other provided set (if mounting on a 365), use H5222X bit.

Mounting screw torque value  9 in-lbs
.  Recheck after 500 rds.

No excess thread locker should be used. You will have to dismount optic to change the battery. Use good, name brand batteries. Not the place to save a few pennies.


Optic I prefer to mount on Sig Sauer XLs?  Holosun HS507K X2.


Sig P320 R2 cut

PRO/AXG/VTAC plates

Plate mounting screws are accessed from top of slide and do have thread locker on them. Suggest use of heat gun or soldering iron to break the bond. If using a heat gun, don't go overboard and exceed the melting point of your striker sleeve.

Current guns should use T20 for mounting plate screws. Older guns may have 5/64th / HX5223X, will have to check my notes.

Note: I do keep a screw extractor setup in a spare drill just for these. I see more than a few after customers unsuccessfully attempted removal.

P320X series R2 and P320X5 Legion R2

Plate mounting screws accessed from bottom of slide. Extractor pin will have to be removed for the extractor side screw. When reinstalling extractor pin, make sure your orientation is correct. The notch on the extractor pin should be facing the center of the slide to properly key with the extractor.

Screw size is 5/64th. Unfortunately, HX5223X does not have the shank length to access the drive. If possible, use a new, unmolested hex/Allen tool for the job.

Romeo1Pro


I like this red dot when used in conjunction with the shroud.  Optic w/ shroud is the default configuration on LE pistols, but not commercial.  

Use T15 for optic mounting screws.

Mounting screw torque value  30 in-lbs.

Use a good name brand battery here.  Be careful not to cross-thread or over tighten battery cap.

The shroud kit is worth the $40 to add to your optic if not equipped. Note that shroud kits may have the Romeo1 mounting screws and not the Romeo1Pro mounting screws. The shrouds work with either optic but the screws are not interchangeable.

Leopold DeltaPoint Pro

This red dot is the tallest of the available options. Sig Sauer tall/suppressor height sights will not co-witness.  Dawson Precision makes an extra tall front sight, and rear if needed, that will work in this application - size is .455T.

RMR footprint

320s made after mid-March 2020 are drilled for the RMR screw pattern. Note that the R2 cut is slightly longer than the RMR footprint optics leaving a gap. Gap can be filled by 3rd party plates.


Sig P320 R1 cut / P320X Five

The original P320 RX, P320X5. Don't see these as much anymore. Firearm does not need to be disassembled but may make it easier to complete the job.

Mounting plate screws accessed from bottom of slide. Extractor pin will have to removed to access second screw. When reinstalling extractor pin, make sure your orientation is correct. The notch on the extractor pin should be facing the center of the slide to properly key with the extractor.

Screw size is 5/64th. Unfortunately, HX5223X does not have the shank length to access the drive. If possible, use a new, unmolested hex/Allen tool for the job.

Romeo1 (original)
Mounting screw is 1/8th / H5225X bit.  Don't recommend these optics because of their poor battery life. Rated 5k hrs, in practice not so much.

Edits: added R2 and R1.
Link Posted: 4/28/2021 12:52:59 PM EDT
[Last Edit: 4/28/2021 12:58:56 PM EDT by l2a3]
I found on my P365XL I needed to slightly loosen the mounting screws on the slide, to allow the red dot to move to zero the pistol. After the red dot was where I wanted it, I then re-tighten the mounting screws on the slide and rechecked the zero. My mounting screws were over tightened originally and the red dot would not move no matter how much I turned the adjustment screws, in fact the silver adjusting screw started to come out on the left side, indicating that something was not working as designed.
The Holosun HS507K X2 on a P365XRomeoZero or XLRomeoZero is a game changer, the only way to go. I love the hell out of it.
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