If you have a Sig Sauer P320, M17, or M18 with an optics ready slide then you are probably wondering which red or green dot sights fit it. In this article we are going to tell you which optics fit it, which ones we recommend, and which adapter plates you need if any.
One of the main things to know about the P320 platform is that since it's release in 2014 there have been different optics cuts. We'll make it easy to understand which optics cut you have, so keep reading.
The optics and adapter plates we recommend will apply to any Sig P320, M17, M18 model that has an optics cut.
Some of the models we are currently aware of that this applies to are the following:
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Is a filler plate necessary for newer P320 Models?
*Tip: if you have a brand new P320 with an optics cut you can mount any RMR footprint optic, however you will need 6-40 screws. We recommend using a filler plate or adapter plate for extra reliability and they come with the screws. To see the RMR footprint optics we recommend scroll down.
- Sig P320 Filler plate for slides with RMR holes and rear sights attached to slide
- Sig P320 Adapter plate for slides with rear sights NOT attached to slide
*Note: If you get the SCS 320 you will not need a filler/adapter plate as long as you have a Romeo 1 Pro Cut Slide.
We recommend a filler plate because mounting an RMR footprint optic to the Sig P320 leaves gaps in the front and rear of the cut and puts all the recoil forces on the screws and you also need 6-40 screws. A filler plate makes contact with the front and rear of the optics cut and provides recoil lugs. This greatly distributes the recoil forces throughout the optic instead of concentrating all the force on the screws.
Step 1: Understand what Slide Cut You Have
Before mounting the optics we recommend you first understand what slide you have. Sig based all their "Optics Cuts" on their Sig Romeo 1 or Sig Romeo 1 Pro optics .. PRO being the keyword. The Romeo 1 came out first, and slides had a flat front. The Romeo 1 PRO came out later and mounted to slides with a curved front. All modern P320 slides have a curved front and come with RMR holes.
*Tip: If your Sig P320 currently has a Romeo 1 or Romeo 1 PRO on it from the factory you can identify the optic by the wording on the sight. If it says Romeo 1 it's a Romeo 1. If it says Romeo 1 Pro then it's a Romeo 1 Pro. You may be able to identify if you have RMR holes by looking underneath the slide.
- Circa 2014-2018 > Romeo 1 Slide Flat Front: This is the first optics cut slide the P320 had, if you bought your P320 between 2014-2018 you might have this slide. If you currently have a "Romeo 1" on your slide, then this is the optics cut you have. If you have a Romeo 1 optic, it will just say "Romeo 1" on the optic.
- Circa 2018-2020 > Romeo 1 Pro Slide no RMR Holes Curved Front: These slides accepted the Romeo 1 Pro optic or a Delta Point Pro (same footprint). They have a curved front instead of a flat. If you bought your P320 between 2018 to 2020 you may have this slide.
- Circa 2020-Present > Romeo 1 Pro Slide with RMR Holes Curved Front: Sig later added RMR holes to the slides, if you bought your P320 from 2020 onward you likely have RMR holes on the slide.
Step 2: Understanding if your rear dovetail sights are wedged in and attached to your slide or if they screw off with optics plate cover
Hopefully by reading above you now know what optics cut slide you have, either the Romeo 1, Romeo 1 PRO with no RMR holes, or the Romeo 1 PRO with RMR Holes.
The next step is to understand if your rear dovetails are wedged in and attached to your slide or if the rear dovetail screws off when you take the optics cover plate off.
Figuring this out is pretty simple, just look at your slide and see if the rear dovetail comes off with the optics cover plate or if they are attached directly to the slide by being wedged in.
*Tip: Most Legion, M18, M17 models have the rear dovetails come off with the optics cover plate. Most P320 LE/Pro, V-TAC, RXP, AXG, XCarry Spectre, Spectre Comp, and some X-Series slides come with dovetails wedge attached to the slide.
Step 3: Understanding the difference between adapter and filler plates.
Ok so now that you know what slide you have, lets talk about adapter or filler plates.
Depending on which slide cut you have, and which optic you want to mount, you'll need either an adapter plate or a filler plate.
If you have RMR holes and want to mount a Trijicon RMR or Holosun RMR footprint optic, then you'll want to use a thin filler plate for extra reliability and security.
If you don't have RMR holes and want to mount an RMR footprint optic, or if you want to mount a Holosun 509T, 507K, or EPS Carry optic then you'll need an adapter plate.
Circa 2020-Present > P320 Romeo 1 Pro Slides with RMR Holes Only - RMR Filler Plates
If you have a slide with RMR holes, you can attach the Holosun RMR footprint optics or the Trijicon RMR directly to the slide, but you will have a gap in the front and the rear. We recommend using the filler plates below because they eliminate this gap, and provide recoil lugs. This gives you extra reliability because with the gap and no recoil lugs all the recoil forces are going directly to your screws which could shear them. Using the filler plate gives you recoil lugs and full contact on the front and rear which distributes the recoil forces through the optic and slide instead of just on the screws.
Below are the two filler plates we recommend. If you have a slide with the rear sights not attached to the slide you can get either version.
- Sig P320 Filler plate for slides with RMR holes and rear sights attached to slide
- Sig P320 Adapter plate for slides with rear sights NOT attached to slide
Circa 2018-2020 > P320 Romeo 1 Pro Slides with no RMR Holes - RMR Adapter Plates
If you have one of the slides that doesn't have RMR holes and want to mount an RMR footprint optic then you will need an adapter plate.
*Note: You can also get your slide milled to add RMR holes by CHPWS or Springer Precision to add the RMR holes. But you will also want a filler plate after that.
You will also want to check to see if your slide has the rear sights attached to the slide or if they are attached to the optic cover plate like the M17/M18/Legion Models
- Sig P320 RMR Adapter plate for slides with no rear sights or rear sights
- Sig P320 RMR Adapter plate for slides with no rear sights only
Circa 2014-2018 > P320 Romeo 1 Slides Only - RMR Adapter Plates
If you have one of the older model P320's with the Romeo 1 cut slide then you will need one of the adapter plates below.
*Note: You can also get your slide milled to a Romeo 1 Pro cut and to add RMR holes by CHPWS or Springer Precision.
Circa 2018-Present > P320 Romeo 1 Pro Slides with or without RMR holes - 509T, 507K, EPS Carry Adapter Plates
If you have a Sig P320 with a Romeo 1 Pro Cut Slide with or without RMR holes then you can use the following adapter plates to mount the enclosed emitter Holosun 509T or the micro optics with the Modified RMSc (K Series) Footprint like the 407K, 507K, EPS, or EPS Carry.
If you are looking for a smaller optic for your P320 the K Series optics like the 407K, 507K, and EPS Carry are very nice choices.
- Holosun 509T to Sig P320 Adapter Plate with Rear Sight (For Slides without Rear Sight Attached Only)
- Holosun 509T to Sig P320 Adapter Plate no Rear Sight (For Slides with or without a Rear Sight Attached)
- Holosun K Series to Sig P320 Adapter Plate (For Slides with or without a Rear Sight Attached)
Best Holosun Red & Green Dot Optics for your Sig P320 (Make sure you know what slide cut you have before purchasing!)
So by now we hope you know what slide you have and understand which adapter plate or filler plate you need. If you don't then make sure you read our guide above, or you can reach out to us on chat.
Below are the top Holosun Optics we recommend for the Sig P320.
Why do we recommend Holosun?
- They are affordable but not cheap.
- They are built sturdily with strong aluminum or titanium housings and glass.
- They have convenient features like Shake Awake and Side Mounted Batteries.
- They have a Limited Lifetime Warranty.
- They are reliable.
- They are waterproof.
1. Holosun SCS 320 Green Dot - Best Direct Fit Enclosed Emitter Recharging Option
*Note: If you get the SCS 320 you will not need a filler/adapter plate as long as you have a Romeo 1 Pro Cut Slide.
Buy the SCS 320 At The Best Price
The Holosun SCS 320 is an awesome new optic from Holosun that comes with a DPP (Delta Point Pro) footprint. This optic is an enclosed emitter and has a green MRS Reticle. It will fit the P320 without the need for filler or adapter plates as long as you have the Romeo 1 Pro optic cut.
What's great about it, is that it uses Holosun's newest "Solar Charging Sight" (SCS) technology. It has an internal rechargeable battery that is constantly getting powered up by the solar panel on the top. The optic consumes power less than it produces it so it can last indefinitely.
The battery has a 20k hour reserve, which means at full charge if it never saw light it would last 20k hours.
This optic has auto brightness settings, and is IPX8 waterproof.
Read our full SCS 320 review here.
2. Holosun 407C Green & Red Dot
Buy the 407C At The Best Price
The most budget friendly option is going to be the 407C. The 407C has a 2 MOA dot only. The housing is aluminum.
If you are ok with having just a 2 MOA dot all the time, then the 407C is a great option.
It has shake awake, a side removable battery, solar failsafe with auto brightness or manual brightness modes, 10 daylight and 2 nightvision settings, and is IP67 waterproof.
Read our full 407C review here.
3. Holosun 507C Green & Red Dot
Buy the 507C At The Best Price
The Holosun 507C is very similar to the 407C except it has Holosun "MRS" reticle.
It's available in Red or Green reticles and the MRS (Multi Reticle System) lets you use a 32 MOA ring + 2 MOA dot, or it can be toggled to show only the 32 MOA Ring or just the 2 MOA dot by holding down the "-" button for 3 seconds.
It has shake awake, a side removable battery, solar failsafe with auto brightness or manual brightness modes, 10 daylight and 2 nightvision settings, and is IP67 waterproof.
Read our full 507C review here.
4. Holosun 507C ACSS Vulcan Green & Red Dot
Buy the 507C ACSS Vulcan At The Best Price
The 507C ACSS Vulcan may pique your interest. It's just like the 507C except is has the ACSS Vulcan reticle. This reticle features a 250 MOA Ring and a 10 MOA chevron - sounds crazy right? Well it's crazy awesome! It helps new red dot shooter and experts alike, and allows for the most precision out of all optics mentioned here.
You can learn more about the ACSS reticle here but to summarize, the 250 MOA Ring helps you find the center dot quickly if you are off center and the 10 MOA chevron acts like a BDC reticle and also has a very precise point for precision work.
It's available in Red or Green reticles and if you wanted to turn the outside ring off you can by holding down the "-" button for 3 seconds.
It has shake awake, a side removable battery, solar failsafe with auto brightness or manual brightness modes, 10 daylight and 2 nightvision settings, and is IP67 waterproof.
Read our full 507C ACSS review here.
5. Holosun 508T Green & Red Dot
Buy the 508T At The Best Price
Next on the list is the Holosun 508T. It's very similar to the 507C except it has a stronger housing made out of titanium and a square window that's a little bigger.
The 508T's square titanium housing is made to give it extra durability, both from the shape and the material.
It's available in Red or Green reticles and they come with Holosun's Multi Reticle System, which is a 32 MOA ring + 2 MOA dot, and can be toggled to show only the 32 MOA Ring or just the 2 MOA dot by holding down the "-" button for 3 seconds.
It has shake awake, a side removable battery, solar failsafe with auto brightness or manual brightness modes, 10 daylight and 2 nightvision settings, and is IP67 waterproof.
Read our full 508T review here.
6. Holosun 507 Comp Green & Red Dot - Largest Window Competition Reticle
Buy the 507 Comp At The Best Price
Next on the list is the Holosun 507 Comp. This is one of the newest and most sought after optics from Holosun. Comp stands for "Competition" because this optic features a VERY large window, meant for competition shooting. It's the largest window in the industry.
The 507 Comp has some key differences vs the other optics listed here. First it has the C.R.S. which is the Complete Reticle System. This gives it many reticle configurations like a 2 MOA Dot only or a 2 MOA dot + 8 or 20 or 32 MOA Circle or just a 8 or 20 or 32 MOA Circle.
The 507 Comp also does not have a solar panel on it which means there is also no auto brightness setting.
It has a 7075 aluminum housing, shake awake, a side removable battery, manual brightness modes, 10 daylight and 2 nightvision settings, and is IP67 waterproof.
This is a large optic.
Read our full 507 Comp review here.
7. Holosun 509T Green & Red Dot
Buy the 509T At The Best Price
The 509T is going to be the most heavy duty pistol optic you can buy from Holosun. It's an enclosed emitter and made with a titanium housing. The titanium is not to make it lightweight, it's to make it more durable.
The 509T comes with and RMR adapter plate but for a cleaner solution we recommend either of these adapter plates depending on your slide cut.
- Holosun 509T to Sig P320 Adapter Plate with Rear Sight (For Slides without Rear Sight Attached Only)
- Holosun 509T to Sig P320 Adapter Plate no Rear Sight (For Slides with or without a Rear Sight Attached)
The enclosed emitter ensures that nothing can obstruct the view of the emitter and the lens, meaning water, dirt, lint or any other molecule will not get inside the optic. It will also make the optic easier to wipe off if it were to drop in mud or something like that.
The 509T is not going to be the lightest optic, but it will be the toughest.
It also has a nice big FOV and is filled with nitrogen which will help with fog-mitigation, just like a scope.
It's available in Red or Green reticles and they come with Holosun's Multi Reticle System, which is a 32 MOA ring + 2 MOA dot, and can be toggled to show only the 32 MOA Ring or just the 2 MOA dot by holding down the "-" button for 3 seconds.
It has shake awake, a side removable battery, solar failsafe with auto brightness or manual brightness modes, 10 daylight and 2 nightvision settings, and is IP67 waterproof.
Read our full 509T review here.
8. Holosun 509 ACSS Vulcan Red
Buy the 509 ACSS Vulcan At The Best Price
Similar to the 509T is the 509 ACSS Vulcan. It is an enclosed emitter optic, but it has two major differences. It’s made out of aluminum and it has the ACSS Reticle (10MOA Chevron + 250 MOA Outer Ring)
- Enclosed Emitter
- Aluminum Housing
- Red ACSS Vulcan Reticle (learn more here)
- 10 MOA Chevron + 250 MOA Outer Ring
- Up to 50,000 Hours Battery Life (Setting 6 Dot Only)
- 12 Brightness Setting: 10 DL & 2 NV Compatible
- Side Battery Compartment
- Auto Brightness Mode or Manual Mode
- Solar Failsafe™
- Shake Awake™
- IP67 Waterproof
9. Holosun EPS & EPS Carry Green & Red Dot
Buy the EPS Carry At The Best Price
I'm throwing the EPS & EPS carry together because they both have the same "K series" footprint. The EPS does come with an RMR adapter plate so you could mount it to the P320 slide or slide with filler plate (as long as you have RMR holes - read above if you need help figuring that out)
To mount the EPS Carry, or to cleanly mount the EPS you will need this adapter plate:
The only difference between the EPS and EPS carry, is that the EPS is bigger.
The EPS is very similar to the 509T in that it's an enclosed emitter optic, but the main difference is that it's made out of aluminum.
Both the EPS and EPS Carry's come in 6 MOA, 2 MOA, or MRS reticles and are available in Red or Green.
Both EPS and EPS Carry's have shake awake and side removable batteries and manual brightness modes.
The MRS versions come with the additional solar failsafe and auto brightness mode features.
The EPS and EPS carry are also IPX8 waterproof vs IP67 like other optics mentioned here and they have 8 daylight and 4 nightvision settings.
Read our full EPS Full Size review here.
Read our full EPS Carry review here.
10. Holosun 507K Green & Red Dot
Buy the 507K At The Best Price
The 507K is one of Holosun's best open reflex micro optics. It's made out of 7075 Aluminum, has the MRS reticle and is available in both red and green. It has shake awake, a side removable battery, long battery life, and is IP67 waterproof.
To mount this you will need this adapter plate:
It does not have a solar failsafe or auto brightness modes.
If you are looking for a sleeker smaller optic with minimal overhang on your slide then this is a great option.
Read our full 507K review here.
11. Holosun 507K ACSS Vulcan Green & Red Dot
Buy the 507K ACSS Vulcan At The Best Price
The 507K ACSS Vulcan is exactly like the 507K except is has the ACSS Vulcan reticle. This reticle has a 230 MOA dotted outer ring and a 3 MOA center dot.
To mount this you will need this adapter plate:
The purpose of this reticle is to help you find the center dot quickly if you are off center. To learn more about the ACSS Vulcan check out our article here.
The dotted outer ring can be turned off by holding down the "-" button for 3 seconds.
The main advantage of the ACSS Vulcan reticle is to be able to find the center dot quickly when drawing the pistol.
All the features are the same as the 507K except for the reticle, and this is available in both red & green.
Read our full 507K ACSS review here.
12. Holosun 407K Green & Red Dot
Buy the 407K At The Best Price
Last but not least is the Holosun 407K. This is the most affordable micro optic Holosun makes and is available in a 6 MOA green or red dot.
To mount this you will need this adapter plate:
The 6 MOA dot is a really nice size. It's big enough to pick up rather easily, but still small enough to be precise with.
It has all the same features as the 507K like side removable battery, shake awake, except is just has a 6 MOA dot instead of the MRS reticle.
Read our full 407K review here.
Choosing between Red or Green Reticles
You may be wondering if you should get a red or green dot reticle. We get this question a lot so I am going to list a few bullet points for you to consider.
- Green reticles are less straining for the eye to see.
- Green reticles can help with astigmatism. If you have astigmatism you will see a blurry dot, we have been told by a few customers that Green dots help with their astigmatism, making the dot look more crisp than the red version.
- Green will not washout on backdrops like green grass, foliage, or green colors.
- In theory Green dots can have a longer battery life because Green is brighter, so for example a green dot on brightness setting 6 may be the same brightness as a red dot on setting 7 - which would save battery life.
If you want to learn more check out our full article about Red vs Green Dot Pros & Cons here.
Choosing between Open vs Closed Emitters
The simplest way we can break down open vs closed emitters is to look at how you plan on carrying the pistol. If you plan on being outdoors in the elements with rain, snow, sleet, then a closed emitter will be beneficial.
If you plan on carrying OWB most of the time and plan on being outside then closed emitter would be beneficial.
If you plan on carrying IWB or don't plan on being outside using your red dot in the pouring rain or heavy snow then an open reflex is fine.
Open reflexes will still work in the rain or snow but the closed emitter will give you extra peace of mind.
An open reflex can collect dust and debris on the inside of the reticle over time, so you'll want to clean it out from time to time. An enclosed emitter is easier to clean in this aspect.
To learn more about Open vs Closed emitters you can check out our Open vs Closed Emitter Guide here.
How to decide which reticle style is best for you
In this guide we covered a few different reticle options. If you need some help deciding which is best for you here are some of our thoughts on each.
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Conclusion
Thanks for reading!
Thank you so much for clearing up the confusion associated with the optics for p-320. There is not much information on the internet especially in the depth that you have. Thank you again.