My CW9 developed a problem where it would fail to return to battery. It would stop about 1/16" shy. Took a while to figure out what the problem was, in part because of that claim by Kahr that the slide only rides on the metal inserts and not the polymer.
Turns out that's not true, at least on the CW9. There is a gap milled in the right rear corner of the slide. When the slide is moved back about 1/16" the insert is in that gap. At that point the insert is not holding the slide. The only thing keeping the pressure from a full mag pushing that corner of the slide up is the polymer rail.
After a large number of rounds (less if your slide was as rough as mine) the poly rail will wear enough to allow the slide to rise when this gap passes and the metal insert gets caught in the gap. That's what is happening with mine. You can actually see the gap between the frame and slide get wider at that point.
I sent this back to Kahr to have it repaired. They replaced the spring, the slide, and the barrel, but didn't fix this. Still does the same thing. The only difference was that I had to fire a number of rounds through it before it started doing it again.
They refuse to acknowledge that this problem exists. They either really believe that "The slide does not ride on the polymer rails at all during cycling, only on the metal inserts both front and rear" or they are deliberately denying a known design flaw for fear of liability. Why they mill all the way into the slide rail slot I can't imagine.
Please don't take it that I'm some kind of Kahr hater. I love my little gun and I will be getting it fixed one way or another. If not, I may pick up a K9 to replace it.