Stripped KE Arms KP-9 Polymer Lower Receiver


WARNING! DO NOT Dry Fire your KP-9 without the upper in place.

Doing this can damage the receiver wall in front of the hammer.

Note: After first range session, remove buffer assembly from lower receiver by pressing down on buffer detent and pulling out buffer and spring. The cycling of the action may have removed additional plastic flash caused by the manufacturing process that was not removed during our post-weld processing. Shake out any debris or use compressed air to clear out the buffer tube.


• The KP-9 has a lifetime warranty for normal use.

• Sling Attachment points wearing out is not grounds for a free receiver replacement.

• If the receiver breaks through misuse or neglect, we will replace it ONCE for $65.00.

• Structural modifications including but not limited to: unauthorized stock shortening, removal of material, and dyeing the receiver void the warranty.

• If you intend to register your KP-9 as an NFA weapon test it thoroughly before doing so in a Title 1 Configuration. Once you Form 1 or Form 2 it, you are legally the manufacturer and we cannot service or support it as easily. Should your receiver require warranty replacement we can only replace it with a title I receiver and we are not responsible for tax stamps or NFA fees.

• Cerakoting: If you intend to have your KP-9 Cerakoted we recommend you use Pro 2 Customs as they are experienced in coating polymer receivers and have our authorization. The bake should be done at low temperatures (<190 Degrees F) and with an upper in place to prevent warping.

Features Include

• 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 rear of 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

Technical Notes

• The KP-9 receiver uses a Carbine LENGTH buffer and spring. A standard 5.4oz 9mm carbine buffer is included in your unit. Do NOT use anything other than 9mm carbine buffers and round springs or the 9mm JP SCSS in the KP-9. Use heavier buffers as long as your gun can cycle reliably. Failure to use this minimum buffer weight of 5.4oz can damage the lower.

• The front lugs where the upper receiver attaches are intentionally snug. The upper should be pushed down in place from the top between the lugs. The rear take down pin may need to be tapped in and out with a hammer depending on upper fit.

• The Take Down and Pivot Pins have the detents built into them; eliminating the spring and detent holes in the lower increases durability. Pins insert left to right. Spare pins are available from KE Arms.

• The buffer detent is held in place with a 5/64” x 1” Roll Pin

• The KP-9 is compatible with cassette style match triggers including the KE Arms SLT units. The retention system of these triggers with D-Clips in the bushings to retain the fire control pins makes them better suited for use in the KP-9 than other designs that require captured pins.

• The hammer pin area is wider for durability. Your receiver includes a special long hammer pin. Standard AR15 hammer pins can still be used but we offer a longer hammer pin for customers preferring a flush pin for aesthetic reasons.

• Your receiver includes a KP-9 Optimized Ambi 90/45 degree selector set to 45 degree mode. Disassembly of the fire control group should only be done by an experienced gunsmith or certified armorer. Safety selector spring and detent load from the top and then the selector is slid over them. Removing the selector arms reveals the easy disassemble notch half way between safe and fire. The selector can be pushed out in this position after the fire control pins have been removed.

• The bolt catch will NOT work for last shot lock back unless you use an upper with a linkage system to interface with the Glock magazine follower.

• The bolt carrier group you use must be one that is machined to clear through Glock magazine feed lips.

Assembly Notes for Gunsmiths and Armorers

Fire Control/Safety Selector Installation.

1) The KP-9 can work with traditional selectors and aftermarket selectors. Installing them is easy. Getting them out usually becomes a Gunsmithing operation that sacrifices the selector in the process.

2) We recommend the use of our Optimized Mil-Spec Selector (Part Number 1-61-02-003) or Optimized Ambi 90/45 Degree Selectors (Wedge 1-61-02-004 or Bar 1-61-02-005) if you want to be able to get your selector back out of the lower easily without damaging it.

3) If all you ever intend to use is Mil-Spec fire control, you can install a normal selector and remove the fire control group for cleaning and maintenance without ever removing the selector.

Fire Control Assembly: General Order of Operations

1) Use the supplied KP-9 Selector Detent. This detent is the same diameter as a traditional selector detent without the rim on the bottom. Detents are available for sale from KE Arms should you lose yours. (Part #1-61-02-006)

2) The selector spring and detent hole is drilled by KE Arms to 0.128” Diameter. This dimension is for your reference should the hole be obstructed with plastic flash during assembly.

3) Place whatever trigger you intend to install in the lower first, but do not install the trigger pin yet.

4) Load the selector spring through the top of the receiver, then load the detent.

5) Insert the selector from the left side and use a punch or other tool to push the detent down into place as you slide the selector over it.

6) Install the trigger pin, then install the hammer/hammer pin.


Bolt Catch Installation

1) The bolt catch plunger should sit roughly even with outer surface of the lower. The hole for the plunger and spring is reamed with a #29 drill. Should you experience plastic flash that was missed in the manufacturing process in this area, spin the drill bit by hand to remove the flash in the hole.

2) Install the bolt catch using a roll pin driver punch only. DO NOT Use Pliers to squeeze the roll pin in. Doing so will damage the lower.

Buffer Detent Installation

1) The buffer detent is held in place with a 5/64 x1” Roll Pin

2) Get the roll pin started by hammering it part of the way in

3) Insert the buffer detent and spring

4) Drive the roll pin in the rest of the way with a hammer and punch while holding the detent down.


1. The buttplate is held on with a ¼-20 x1” Screw (top) and a 10-32 x 1” Screw (bottom)

2. A1 and A2 Buttplates can work with the KP-9 but some fitting may be required

3. Look for more buttplate options on in the future.


Magazines NOT locking in OR Upper CANNOT Close

1) Loosen the screws that retain the ejector on the left side of the receiver

2) Insert an empty magazine

3) Close the upper onto the lower

4) The Ejector should now be centered between the top of your magazine and the bottom of the bolt carrier group, allowing magazines to lock in, and the upper to close and the bolt carrier to move freely

5) Tighten the screws that retain the ejector

Upper still CANNOT close or Bolt Carrier will not move

Though we strive for as much cross compatibility as possible, unfortunately there is no industry wide spec for Glock magazine fed 9mm AR15s. Some bolt carrier groups have a track that is too narrow for our ejector or the track is offset vs the ejector location. In these cases the ejector can be fitted to the particular bolt group and will run properly with sufficient clearance. Contact KE Arms at for further guidance/instruction.