One Piece Poly Lower

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I received my KE Arms KP-15 lower on Friday and have assembled it. I purchased knowing there’d be some compromises, but wanted the weight reduction as I am using this on a pencil-barrel, 5.56 lightweight build. I haven’t shot it yet but here are my thoughts thus far.

It’s light. I weighed a standard Aero Gen II carbine lower with Magpul CTR stock. It came in at 38 oz. The KP-15 with the same trigger and buffer was 29 oz. I don’t know how else to save that kind of weight on a lower without spending $$$. Yes, there are lighter stocks than the CTR but it’s no heavy weight either.

You can assemble a stripped KP-15 lower with a standard lower parts kit. However, there are some propriety parts included with the KP-15 lower. Here’s what unique to this lower:

Take down pins
Take down pins are not stock pins and are NOT captured. They have the detents built into them and the lower is not drilled for standard springs and detents. I consider this the biggest con of the lower. To access your BCG, you end up with a pin in your hand. Don’t lose it! If you transport your AR-15 with upper and lower separated, you’ll have the added step of pulling pins, putting the rifle together and then re-installing pins. The pins come with the lower and spares are available from KE Arms.

Safety selector detent
The safety spring and detent are loaded from the top, not underneath the grip as on a standard lower. You can use a standard safety lever (I did) but removing it will require drilling it out. KE Arms offers a selection of safeties modified to work with the lower to ease removal. They also provide a proprietary detent. The spring from a standard LPK is used.

Buffer detent retention
The KP-15 does not use a buffer tube. The buffer and spring ride in a hollow in the stock.
The detent and spring are retained by a 5/64” x 1” roll pin (provided). I didn’t install this as I’m using a JP silent capture spring.

There is storage in the stock but it requires tools to access it. There’s no hinged butt plate like an A1 or A2 stock. KE Arms claims A1 and A2 butt plates will work but “may require some fitting”.

Most cassette-style triggers will not fit. My CMC did not. It appears the polymer is thicker and rounded where the trigger well meets the wall of the magazine well. I fitted the CMC by grinding down the front edge of the CMC housing to gain the clearance I needed, probably under 1/32”. Not the most elegant of solutions but I had it on hand and really didn’t want to spring for another trigger.

Here’s the page with detailed information about the pros, cons and assembly of the lower.
KP-15 Stripped Instruction Sheet (kearms.com)

I noticed Brownells is asking $109 for these now. I paid $89 when I pre-ordered. Considering it’s weight, strength, and the fact that you’re not purchasing a grip or buffer tube I thought it was a good price.

Good explanation on the lower and a few of it's peculiarities. Overall I like mine, it's very light as you said, and stiff. Finally got it out on the range last week and ran maybe 20 rds through it to check the gas block setting, everything worked and shot just fine. If you already have a handful of ARs like most folks do, I really don't see any realistic downside to picking up a unique but well done monolithic lower like this for a specific purpose.