Product Review: the KP-15 AR Lower

In this post I’m going to review a new addition to my collection, the KP-15 AR lower receiver by KE Arms. This is basically a slightly updated version of the receiver Ian and Karl used for their What Would Stoner Do? rifle project for InRange TV.

The KP-15 is a Monolithic Polymer AR which incorporates the lower receiver, pistol grip and trigger guard, buffer tube, and stock into a single unit made from injection molded, 30% glass-filled nylon. This is a direct follow-on to the Cavalry Arms vibration-welded lowers, which themselves were a development of the much earlier plastic or polymer monolithic lowers that Colt experimented with all the way back in the late 1960s early 1970s. Ian goes into more detail on this history in this excellent video.

When I received the box from my transferring FFL, my first thought was “Is there anything in this?” It feels so much lighter than a complete traditional lower receiver with pistol grip and stock that the box felt empty. In fact, the whole thing weighs about seven or eight ounces less than my aluminum lower assembly.

The author's first view of his new KP-15

After unboxing and handling my new receiver I found that, while lighter, it was comfortable and handled very well. I think the stock being A1 length helps with this; the A2 stock is about 5/8” longer, which does make a noticeable difference. My wife, who is five foot two and petite, also found it comfortable if a little long for her.

There are a few differences to be aware of between the KP-15 and traditional lower receivers. First, the takedown and pivot pins are inserted and removed from the left side of the receiver instead of the right. They’re also not retained pins, but rather come all the way out. To keep them in the receiver, the pins have ball detents built into them, which means there are fewer additional holes in the receiver for the pin springs and detents.

A closer view of the KP-15 takedown and pivot pins

The selector spring and detent are installed from the top and the selector lever is inserted above them. Again this simplifies the receiver, but makes it harder, possibly much harder, to add an aftermarket safety. (KE Arms recommends using one of their selectors. They also offer a variety of accessories for the KP-15 lower.) Since I bought the complete lower, I was able to take a look at the internals and it appears that the only difference is a bevel on the right side selector pivot to make removal easier. The bevel is not in alignment with either the safe or fire position to reduce the chance of the lever coming out unintentionally. I filed a similar but smaller bevel on the ambi selector I already owned.

Even though the KP-15 has an A1 length stock, it takes a carbine buffer and spring. This allows for more thickness of material at the back of the stock for strength. It also seems quieter during recoil; there was very little of the traditional AR sproing through my cheekbone. The difference in felt recoil was negligible, however, and I’m honestly not sure if there was any. While the aluminum receiver is heavier, the polymer receiver flexes slightly, which draws the recoil out over a greater duration.

What was noticeably different was the balance: my nice compact AR carbine is now markedly muzzle heavy. Since I already have a pencil-weight barrel on this rifle, it looks like I’ll have to buy a new light weight fore-end to rectify this situation. Such a tragedy.

The current setup of the author's rifle

I’m considering a Midwest industries free float handguard, either the seven or fourteen inch version. They look very nice and the smaller one weighs less than seven ounces, compared to my current handguard which is an older quad rail that weighs almost 12 ounces. That should nicely shift the balance back towards the magwell. Another, more expensive solution would be to file paperwork with the ATF and SBR the barrel, but I’m unlikely to go that route at this time.

In conclusion, if you’re considering a KP-15 lower, either stripped or complete, and assuming they’re in stock and legal in your jurisdiction, I can say "Buy with confidence."