MP17 Review – Flux Defense MP17 PDW For Sig P320

by Ryan Cleckner

February 4, 2022



In this Flux Defense MP17 review, we’re going to cover what the MP17 is (and what it isn’t). First, the Flux Defense MP17 is NOT a firearm and the sample we tested isn’t a rifle either. It is, however, a really novel concept on the PDW platform.

We’ll give you a hint about what we think about the MP17: We LOVE it. But, it had to grow on us first. Read on to see what we mean.

MP17 Specs

  • Host Platform Sig p320
  • Caliber 9mm
  • Magazines P320 Mags
  • Weight 2.8 lbs
  • Length (collapsed) 10.75’’
  • Width 1.6’’
  • Height 5.75’’
  • Capacity 38 rounds

Flux Defense MP17 Background

PDWs are very popular now. It seems like the industry is flooded with 9mm carbines. And why not? They’re a ton of fun to shoot, low recoil, compact/concealable, and they shoot inexpensive ammo.

Also, the PDW (Personal Defense Weapon) style is popular with executive protection teams.

However, most 9mm carbines/PDWs are dedicated platforms that don’t share anything in common with a sidearm. The problem with this is, especially in a tactical scenario, lack of commonality of parts and magazines.

If a soldier or officer has a 9mm PDW, there’s a good chance that they have to carry two different types of magazines for their PDW and sidearm. Also, parts between the two are not interchangeable.

Flux Defense solved these problems and more. By making a platform for a firearm (and not a firearm itself), the MP17 can take the guts of a Sig p320 and it uses p320 magazines.

This means that most parts between a completed MP17 and Sig 320 are interchangeable and the magazines can be used in both!

It’s a really novel idea by Flux Defense. But, does it work?

Flux MP17 Features

1 Light and Compact PDW-Style Chassis

Makes the MP17 quite possibly the best PDW platform.

2 Extra Magazine Storage

Allows 38 round capacity on-board with factory mags.

3 Spring Loaded Arm Brace

Collapses for a small footprint and deploys quickly with one finger.

4 Optics Ready

Mounting options for all major red-dots and even a picatinny rail.

Flux Defense MP17 Review – Our Take

The Flux Defense crew sent us an MP17 (pistol brace version) for us to review.

Full disclosure: My first thought upon seeing the MP17 online was…. “huh?”

I couldn’t understand why someone would put all of that…stuff… onto a Sig P320. Once I realized that it wasn’t adding things to a p320 but rather it was its own thing, that is the smallest and lightest 9mm carbine-style platform available that used readily available parts and magazines, with some p320 parts inside, I saw its genius.

Seriously. It may not look like what you expect to see but it is AWESOME.

Here’s how I look at this novel platform (seriously Flux Defense crew, kudos on thinking outside the box and taking advantage of the p320 modularity): If you’re looking for a 9mm carbine-style firearm, you probably want it to be small and light. You also probably don’t want to purchase expensive proprietary magazines (or an expensive firearm for that matter). Also, you might be concerned about the reliability of the platform.

Well, with the Flux Defense MP17, you get the lightest, smallest, and least expensive PDW (9mm carbine style firearm) that uses the same operating components as the pistol selected by all branches of the military for its reliability and it uses the same magazines that are readily available (and that may also work in your sidearm).


Before I took the MP17 to the range, installed a p320 mag release, the chassis from my x-compact, and a full-length p320 slide. The chassis was a bit tough to get in the first few times I tried. I think this is due to a tight fit in the plastic housing and learning to get the slide releases easily between the MP17’s support bars.

I then took an RMR off of one of my pistols and went to install it on the MP17 and started to curse the Flux Defense crew. The flat top of the MP17 meant that my RMR mounting screws were too short. I mumbled to myself that they should have included the right length screws for their special platform and right as I moved the box it came in…. you guessed it… I found the screws they included for all the major red-dot platforms. Oops. Maybe I should read the instructions and check all the parts before I get frustrated.

I took the Mp17 out to the range to put it through its paces and I’ve taken it a few more times since because it is so fun to shoot.

What I Liked:

The MP17 is the smallest, lightest, and least expensive system in its class. For example, CZ Scorpions, Sig MPXs, and AR-style 9mm platforms are larger, heavier, and more expensive than the MP17. Check out my short video above to see how tiny the MP17 is and how it fits in the tiny back pocket of my bag.

The MP17 is super fun to shoot. It isn’t just a great platform for me, it’s easy and fun for smaller-framed shooters like women and children too.

There’s tons of firepower (almost 40 rounds with factory magazines onboard) with magazines from your pistol (if you shoot a p320) as backups.

I can’t get over how great it is that I can use the same spare parts and magazines for my MP17 as I can for my p320. I know that the Army recently selected the B&T 9mm PDW, in part because it took p320 magazines. I really wish the Army took the MP17 instead – the military is all about supply chain and uniformity. This would make it easier for logistics and soldiers! And, it comes with a holster (see below)!

The MP17 made me more accurate and allowed me to shoot faster than I can with just a standard p320. But, not by much. I’ve been practicing handgun a lot lately and I’d say it gives me a 10% speed increase for any particular drill. However, even though it isn’t a major change, the confidence and accuracy in my shots make me that much better. Also, as I’ll touch on below, it made a bigger difference for less experienced shooters.

Although it’s not a rifle, I could still shoot the MP17 further than I can reliably shoot with just a handgun. Just for fun, we were repeatedly smacking a silhouette at 200 yards.

You can tell that the Flux Defense crew really thought this thing through – they even have a window in the housing that allows a shooter to use the slide’s iron sights if needed.

Also, the spring-loaded arm brace is not only fast to deploy, but it’s also a lot of fun (don’t judge me).

What I didn’t Like:

I wish the MP17 came with a p320 mag release installed. This is the only part that keeps the MP17 from being an easy swap from pistol to PDW. Well, it’s still fairly easy, but it’s not as simple as it could be if it came with this small part.

I’m fairly tall (and have a big head) so the pistol brace is a bit on the short side for me to shoulder (my face is closer than I’d like but this isn’t a rifle, it’s a super-compact PDW).

I really like to use a slide release (yes, I call it a slide release… you can “correct me” in the comments below) and the MP17 is designed in such a way that it doesn’t allow access to the p320 slide release. This isn’t poor design, I think it is just not feasible.

The one thing I asked them to improve was the spare mag holder. They already mentioned that they’ve improved it and that I have an earlier model/prototype. The spare mag holds in place with friction and can be very difficult to remove. Ideally, I’d like to see another p320 mag release included but mounted on the other side (might as well take advantage of the ambidextrous features) so it’s not so easy to accidentally engage.


So, how small is it? When the brace is collapsed, the MP17 fits into my favorite pistol safe, the Fort Knox PB1. That makes this about 100 times better for home defense than just a handgun!

If you’re looking for a 9mm carbine-like platform, and especially if you already have a p320, you’ve got to give the Flux Defense MP17 a look. It’s lighter, smaller, and less expensive than anything else and it ran with flawless reliability for me and it uses commonly found parts and mags.

What’s not to love?

Now, be honest, did I change your opinion at all? Let me know in the comments.

Although the MP17 can be used with any small-frame (9mm, 357 sig, or 40 S&W) slide, any slide shorter than full length should be used with a compensator for safety.

Flux Defense MP17 Pros and Cons

  • Super light
  • Super small
  • Reliable and fun
  • P320 parts commonality
  • True innovation (nice to see in the firearms industry)
  • Doesn’t include mag release
  • A bit short (but, it’s supposed to be)
  • Can’t access slide release
  • Awkward spare mag storage

Report Card


Flawless reliability (approximately 1,500 rounds of Magtech 9mm shot so far).


Peak accuracy from a p320 platform. It’s not a rifle, but it lets you stretch out farther and more accurate shots than you could likely do with a pistol alone.


The MP17 made me a bit faster and more accurate than a p320 alone. However, when I gave it to some fairly novice shooters, their abilities improved a LOT with the MP17.


I love how they designed the MP17 – it is very intuitive to hold and use. However, it’s a bit too short for me, the housing pushes my firing hand lower than I’d like, the spare mag holder isn’t ideal, and I wish the slide release was accessible.


For the money, the MP17 can’t be beat. Even if it cost more, I still think it’d be a great value for what it is… the simplest, smallest, and lightest PDW.


Our Grade


Reviewed by Ryan Cleckner

Reader’s Grade


Based on 7 Reviews

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The Flux Defense MP17 is an AMAZING PDW suitable for any budget. But owning one doesn’t just mean you have everything you need. So if and when you purchase one, you can be ready to start shooting. Here are some key essentials.

And while we LOVE THIS GUN fresh out of the box, there’s always room for an upgrade or two for the Flux Defense MP17.

MP17 Compared to Other 9MM Platforms

FeatureMP17Sig MPX CopperheadCZ Scorpion EVOAR-15 9mm PDW
MSRP$399 ($899 w/ p320)$1749$929$1,200-1,900
Caliber9mm9mm 9mm9mm
Weight2.8 lbs4.5 lbs5 lbs5 lbs
Barrel Length4.7 in3.5 in7.75 in4.5 in
Length (Collapsed)10.75 in14.5 in16 in19 in
Width1.6 in2.4 in2.0 in2 in
Height6 in8 in10.31 in7.2 in

Best Sights for the Flux Defense MP17

How do you take one of our favorite guns and make it even better? That’s pretty simple. Put a red dot on it. Now, keep in mind when choosing a red dot for the MP17, you’re very limited on your red dot options and compatibility. Here are the two main choices you have when installing optics onto your Flux Defense MP17.

Our Editor’s choice for sights goes to the Romeo1 Pro. Not only is it designed to go on the MP17 without any adapter plate, but it’s also a crazy good sight. The Romeo1 Pro comes in a 3 MOA or 6 MOA model–both of which co-witness with the front sight. Just be sure you’re getting the PRO model. Or things aren’t going to fit the way they need to. CHECK PRICE

This standby optic is fantastic for just about any gun, and you really can’t go wrong with it. The Leupold DeltaPoint Pro is one of those go-to sights, when it comes to red dot sights. It’s got an extremely clear and large lens, with a 2.5 MOA red dot. For mem this one is up there as the most rugged options around.

Check It Out on Amazon

Other Pistols of its Class to Check Out

While we may love the MP17, you might hate it. I mean I doubt it, but there’s always a slight chance. So just in case, you are one of those that do not like it and prefer something different, here’s an alternative you may find to be better suited to your liking.

#1 Sig Sauer P320 X-Five Legion

Check Latest Price

  • Shootability A+
  • Reliability A+
  • Ergonomics A+
  • Accuracy A+
  • Value A+

Our Grade


Reader’s Grade


Based on 54 Reviews

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We’ve reviewed a ton of guns here…but this one is most likely our absolute favorite. And I’m not just talking about handguns either. Probably our favorite ever. Testing it for competition and as a range pistol, we couldn’t find a single thing wrong with it. …READ MORE

How to Care for Your Flux Defense MP17

Field stripping, maintenance, and cleaning should be standard knowledge to know about your gun. In this video, you’ll see not only how to assemble the Flux Defense MP17, but how to operate it. And I mean completely. This is a super informative video to learn more in-depth about your MP17.


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About Ryan Cleckner

Ryan is a former special operations sniper (1/75 Ranger) and current firearms attorney, firearms industry executive, university lecturer, and bestselling author of the Long Range Shooting Handbook.

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  1. I have this Raider in 9mm and works great with a slide adapter on the side of the slide. My only way to transport this is in a bag with several 21 round mags. It has no holster!!!

  2. Does this MP17 Flux (or any for that matter) work with the XFive Legion P320. It is not clear what models DO not work that one might believe does.

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