There is no doubt in my mind that Russell Phagan, the WWSD 2020 project, and KE Arms are largely responsible for the recent revival in interest concerning monolithic polymer lower receivers for AR-15 rifles. The KP-15 started hitting customer’s front doors around the start of 2021 and the subsequent bum rush of parts related to the WWSD 2020 project dried up pretty quickly leading to many taking their own routes for uppers. Just a hair over a year later, KE Arms gave fans of the KP-15 another reason to pick up another lower, but this time with a 9mm PCC in mind. The KE Arms KP-9 monolithic polymer lower receiver is the 9mm pistol caliber carbine cousin of the KP-15. The KP-9 is a logical extension to KE Arms’ list of receiver options and I’ve been lucky enough to be able to test one of these out for the better part of a year. Today I’ll share my experiences with it so far and what I think the KP-9 lower receiver offers PCC customers over other offerings already on the market.

More from KE Arms @ TFB:

• KE Arms Announces Glock Mag-Fed KP-9 Polymer Receiver
• KE Arms Introduces the Improved Rekluse RTS-2 Trigger
• GWACS v KE Arms Update: Majority of Causes of Actions Dismissed

TFB Review: The KE Arms KP-9 – The KP-15’s 9mm PCC Cousin

The KP-9 is a direct descendant of KE Arms’ KE-9 billet lower receivers. Like the KE-9, the KP-9 not only takes glock mags, but it’s also partially ambidextrous via a cleverly integrated left-side magazine release that doesn’t sit above the frame of the lower meaning you won’t accidentally bump it running around with the gun slung. Like the KP-15 lower receiver, the KP-9 is lighter in weight compared to similarly configured 9mm billet receivers, costs less, and is made from a tough injection molded 30% glass-filled nylon polymer that makes up the entirety of the KP-9’s body.

The KP-9 lower we’ll be reviewing today is one that is specifically kitted out by KE Arms on their site and as such it’s one that you can buy without having to assemble it yourself (not that it’s particularly hard). Below is a list of its features, including all of the upgrades made to it at the KE Arms factory. This iteration of the KP-9 lower costs $559.95 and can be upgraded further with a trapdoor buttplate. If you want a plain stripped version where you can add your own fire control group, that will only set you back $159.95.

This particular model weighs just under 2 lbs with the included buffer, spring, trigger, and one M-LOK QD sling socket I added to the back right-hand side of the stock.

Features Include:

• Compatibility with most common 9mm AR15 uppers and lower parts kits
• Compatible with Glock 17 and 19 Magazines
• Flared magwell to make reloads under stress easier to perform.
• A1 Length 13” Length of Pull (LOP) Buttstock to fit a wide range of shooters
• MLOK Slots at the rear of the stock for sling attachment points or run a strap through it for simple sling attachment
• Holes at the front of the stock for QD socket inserts for more sling attachment options
• Improved grip for comfortable use
• “Winter” Trigger Guard

Rekluse Trigger Lowers Include:

• RTS-1 REKLUSE Trigger
• Ambi Optimized Selector
• 5.4oz 9mm Heavy Buffer and Spring
• Bolt Catch Assembly*
• Pivot and Take Down Pins
• KP-9 Selector Detent
• Buttplate
• 5/64″ Roll Pin to Retain Buffer Detent
• Ambi Glock Magazine Catch Assembly
• Adjustable 9mm Steel Ejector

Materials Quality/Construction

The biggest concern most people have with polymer lower receivers seems to circle around durability. Glass-filled nylon polymers are pretty dang tough – it’s why Magpul PMAGs are the most popular polymer magazine on the planet. The KP-9’s materials quality is just as good as the KP-15’s, it’s made from the exact same blend of glass-filled nylon using the same molding techniques that Russel and his team at KE Arms have perfected.

If you’re persnickety about having your firearms be in perfect machine tolerance, the KP-9 lower won’t impress you as like with its predecessor KP-15, the KP-9’s injection molded nature means that parts have to be trimmed, flattened, and deburred to make it look somewhat presentable. These uneven seams are a byproduct of the joining process from the two halves of the KP-9 being sonically welded together. You’ll find that most of these spots are a tad bit uneven when looked at closely but to me, this is just a necessity of the design and doesn’t impact performance so I’m okay with it. Most of these uneven markings and textures can be remedied by just Cerakoting the lower which I’ve seen plenty of people do.

Range Experiences

Over the course of the year, I’ve brought the KP-9 with me to a lot of range sessions to test it with mags and different uppers, used it in the PCC division of several muti-gun competitions, and also had plenty of time to mag dump and bump fire it to test its tolerance for malfunctions and different types and styles of ammunition. The KP-9 is probably going to be seen a lot more when it comes to any of my 9mm PCC reviews (including one coming up on the Angstadt Arms 9mm 16″ Upper), this is simply because I enjoy the length of pull, and how light it is, and of course how durable it has been.

One point of failure that is common on a lot of 9mm AR-9 lowers is the ejector. I’ve seen several ejectors become bent over time and this inevitably leads to malfunctions that will quickly end a range trip. The ejector included on the KP-9 lower is made from some pretty tough steel and although it’s adjustable, I’ve never felt the need to reposition it or tighten it over the several thousand rounds shot using this lower.

The ambidextrous controls are quite handy, especially since it’s much easier to grip Glock magazines with one hand. I will say that I still much prefer the Colt-style magazine as I find it is much more natural to perform reloads with them, however, the KP-9 partially solves this frustration with a beveled and flared magwell. As you can see on my magwell, the polymer does tend to still get banged up around the edges but has more or less held up very well for how much I’ve shot it.

The Rekluse RTS-1 Trigger

The REKLUSE RTS-1 Trigger has fast become my favorite cassette-style drop-in trigger. The REKLUSE features an enclosed design that keeps dust, dirt, and carbon fouling from entering the critical moving components, and therefore the trigger always has a consistent feeling and safe 4.5 lb pull. While some people may malign the triggers shoe appearance, I think it looks alright if not a bit on the “edgy” side but who cares, you’re pressing it not looking at it.

The REKLUSE allegedly aids in more efficient cycling since the trigger features no disconnector for the hammer to drive through, this means there’s less resistance for the bolt to push through and you can better isolate cycling issues to other components. The RTS-1, although it comes in the KP-9, can be dropped into virtually any other 9mm AR-style PCC lower as well as the SIG Sauer MPX.

My favorite feature about the RTS-1 trigger is the ability for you to switch the firearm back to “safe” without having to re-cock the hammer. Due to the unique geometry of the trigger, the safety can always be applied regardless of the hammer being down or cocked. When used appropriately, this adds another level of safety to administrative handling and clearing of malfunctions and it’s something that I know is very common and sometimes even a requirement in European military rifle contracts.

Final Thoughts

I think the KP-9 still stands as the best polymer 9mm lower receiver option on the market. While it suffers in the same areas other polymer lower receivers do, in the appearance department, I find that the combination of a classic stock design, and monolithic construction make the whole package so lightweight and durable that I don’t really care about the looks anymore – besides that, the A1 style of stock will never get old and will always look cool. The inclusion of some ambidextrous features but not others and the absence of sling hardware is kind of curious to me for something as expensive as this particular KP-9 was, but I do have to admit that a majority of that extra cost is going into the RTS-1 REKLUSE trigger which sells for $289.95 – literally half the cost of the rest of the lower and its included parts.

I would say that if you’re in the market for a lightweight 9mm PCC for either a camp gun or a competition gun, the base model KP-9 lower receiver is a great place to start. The RTS-1 trigger is a very expensive but very worthwhile upgrade if you like single-stage triggers but at nearly $300, I think that will be a stretch for most people’s budget. The prowess of the KP-9’s design lies in its affordability at around $150, making it less expensive than even a stripped PSA 9mm Glock lower, but already includes the stock.

I’d of course like to hear your thoughts on the KE Arms KP-9 polymer lower receiver. What do you think of the concept of having an entirely polymer lower receiver? Let me know if you have any questions about the KP-9 polymer lower receiver as well as your thoughts on it down below!

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