OK, I made it through two entire matches now with only one jam, so I think the Mimber Mag issue can be laid to rest.
You just have to file down the ridge on top of the feed lips, if there is one, and it works.
Here are the last two mags I bought:
Three of the five mags I have, including the one that came with the slide, looked like the first picture when new. Two looked like the second picture.
Now they all look like the second picture...
