What upper should I use with the KE-9 or KP-9?

We have successfully used uppers from the following companies.  Make sure the bolt carrier is machined to clear Glock magazines.

CMMG (Blowback uppers only not Radially Delayed)
FM Products
JP Enterprises
New Frontier Armory
Gibbz
Aero Precision

Follow the ejector height adjustment procedure to set the height of the ejector to your bolt.

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