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  • Post last modified:June 14, 2020

P90 side view garand thumb

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The FN P90 is a very special 5.7mm PDW (Personal Defense Weapon), and it's even selected as one of the primary Secret Service weapons for its low profile, lightweight, high round capacity, and rate of fire capabilities.

Finding a quality optic for the P90 isn't the hardest thing in the world, and in this post, and the best red dot sights for FN P90 we recommend is a low profile red dot sights like the Trijicon RMR/SRO or Aimpoint Micro on a low mount by Design Machine Inc. we will also share with you the best mounts at the end of this post for your P90 upgrade.

Read More: Best Red Dot Sights

Best Red Dot Sights for FN P90 (Low Profile Sights)

best red dot sights for FN p90 submachine gun

FN used to make PS90 USG red dot sight that is integrated with the top front part of the gun, now it's discontinued, but where are other things you can get.

Related Content: Best Red Dot Sights for PCC

What To Look For In An Optic for FN P90

Low Profile Design Machine P90 red dot sight mount

Image Referenced Design Machine Inc

The FN P90 is designed for close-quarter combat in the 1980s with its effective 5.7mm cartridge. Its 50 rd magazine and fast rate of fire make it a perfect PDW (Personal Defense Weapon).

Using the PS90 iron sight isn't a practical way to shoot this gun, so having a red dot sight is the way to go for faster target acquisition and wider situational awareness.

Here are a few things you should consider when purchasing an optic for P90.

  • Keep the optic size small
  • Find a secure & compatible low mount
  • Lightweight
  • Large field of view

Use Design Machine Inc Aftermarket FN P90 Optic Mounts

FN P90 Design Machine INC low optic mounts

Image Referenced Design Machine INC

Generally speaking by default, the P90 optic is mounted very high over the bore, and that's the problem we have to deal with based on its original design.

The plan is to remove the original Picatinny rail adapter and replaces it with one of the Design Machine Inc's mounts.

Reticle Size Selection for P90

Red Dot Sight MOA Sizes

You got the P90 because you value its close-quarter capability, therefore a 2 to 5 MOA dot size is perfect for the P90 for close-range shooting.

Usually, a super-fine 1 MOA size dot is great for long distance precision.

A big 5 MOA size red dot from the Trijicon SRO gives you about a 5″ shot group at 100 yards, and this can also be beneficial for acquiring the sight much faster.

Does The P90 Sight Sit Too High Over The Bore?

p90 sight height over bore issue

Image Referenced Iraqveteran8888

The average sight over height distance is about 3 inches, and we would want to reduce that distance as far as we can.

The most popular P90 RDS configurations are the use of aftermarket optic adapters that slide inside the top section of the gun, which lowers the optic height significantly.

We like configurations where the optic sits low on the gun. Design Machine Inc has great mounts for various optics like the Aimpoint ACRO P-1, Aimpoint Micro, HoloSun, Vortex optics…etc.

Even with the lowest profile red dot sight, the height over bore distance is about 4 – 5″.

That's ALOT!

By default YES! the optic on the P90 sits VERY high on the gun, which means there are new holdover techniques for you to master for this gun.

In addition, make sure you pick an optic that has a wide windage and elevation adjustment range something like 100 or more MOA total travel, otherwise, you will max out your adjustment and would still not be enough for the zero.

What Distance Should I Zero My Optic on The P90?

The best distance to zero the gun is 20 – 50 yards for close quarter shooting. With a standard NATO SS197 5.7 x 28mm 40-grain bullet, it can effectively deliver up to 2350 ft/s muzzle velocity that can reach 150 – 200 meters.

Whether you're using the standard 16″ barrel or the short barrel this is the best distance to zero it.

Since the P90 has a significant height over bore issue, zeroing at 50 yards where the point of aim is the point of impact, and the holdover is about 3-4″ for anything within 10 yards.

So all you have to do it aim high for close-range targets, and this is very important for you to use a PS90 low profile red dot mount to minimize the holdover as much as possible.

With the lowest mount using the Design Machine Inc RMR fixed mount, you lower the sight height by almost 2″, which also shrinks the amount of holdover distance.

The less you have to measure or compensate for holdover, the faster and easier target acquisition would be for you while shooting close-range targets.

PS90 Secret Service Sights In Use Today

USG secret service P90 with Aimpoint

Image Referenced MilitaryWiki

The U.S. Secret Service is one of the FN P90 users among over 40 nations.  The FN P90 USG (US Government) model has an integrated red dot sight, however, that was upgraded to the Picatinny rail mount for more optic flexibility.

Based on the community information, they now use the P90 flat top rail for Aimpoint and other optics.

This is one of the exciting things everyone wants to know, however, they don't typically openly publish their loadout on the internet unless we happen to see it.

Round Up

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P90 is an unique fast rate of fire 5.7 x 28mm submachine gun designed for close quarter combat. Part of its capability comes from the high-velocity cartridge, which has the ability to penetrate Kevlar protective vests, and its unique top feeding 50 round magazine.

Because the top feeding magazine occupied much of the space for mounting an optic on the P90, the sight height over bore is very high for almost 5 inches with the default flat top rail.

Picking a low profile sight like the Trijicon SRO on a low mount from Design Machine Inc can significantly reduce the vertical profile of the gun by 1-2″, and make it more holdover friendly.

Pairing the gun with a 2 MOA dot or a large dot size gives the shooter a more visible reticle to pick up, for fast target acquisition and wider situational awareness.