Re: New P3AT owner - sad news
The problem with mine was the floor plate. I had already trimmed the flash off the top, but that still did not allow the magazine to enter far enough to engage the latch.
Starting at the beginning, all three magazines fit in the P3AT, but after firing each magazine a few times, first one and then the others would apparently snap in but fall out during firing. A call to K-T had a replacement latch to me in a few days. Then I found that only 2 of the 3 magazines would latch with the new latch. While waiting for the replacement, I read on this forum that the latch needs to be held in while inserting the magazine, so the new latch has been treated gently.
I swapped floor plates, and the problem followed the floor plate. Inspecting the two, there was no apparent difference; in fact the good one did not have the flash trimmed so it looked the less likely to function. Measurements on the open end of the floor plates were nearly identical. But the depth of the floor plate groove on the closed, rounded end was different by 0.020". Refitting showed no interference on the open end of the floor plate to the grip, but there was interference to the grip on the rounded end. Careful slicing with a utility knife and smoothing with a file on the top of the rounded end to remove about 0.020" gave the desired result. No material was removed on the half with the open end.
My suspicion is that the problem magazine was the original and that the latch may have been "adjusted" to hold the magazine, but the latch ended up angled, and the magazines falling out numerous times kept taking a little more plastic off the latch. I could locate no cavity identification on the floor plate, but the mold core apparently got loose or bent so the groove for the magazine is too low.
Sorry for the belated (and extremely dry :-[) report. But it is a simple matter to remove the floor plate and take off a little plastic.
G2S