Ill tell you what happened. Since I was the guy that worked on them.
The tool to make them was a single cavity with a pull core for the internal part of the mag. Now the pull core, for those that don't already know, is a sliding core that forms the inside of the part. In this case the pull core formed everything inside up until the feed lips. Because it is pulled out it has to have draft to it to allow it to come out easily. There was a big debate between myself, Tony and the toolmaker on how much draft should be put on this component. Both the toolmaker and I wanted to have as little as possible to keep the gaps small. Tony didn't believe this was possible.
I won, we put very little draft on the part (similar to the pmag). However, the toolmaker subcontracted this part out to another tool shop where it was made....very poorly. The surfaces were wavy (+ .004"ish) which meant that as the core was pulled, it expanded the mag itself. This expantion allowed the rounds to essentially fall off the follower. You will probably find videos of people loading their mags and take the top 2 out and then it stops feeding. Well that was the problem.
After some time I found the problem and had the original toolmaker fix it. This was around June/July 09. We tested them in numerous lowers. Dave was part of that actually. And we had no problems. The materials that go into the mag are very hot during the molding process and if the core and the tool itself is not properly maintained it would change shape. This is what I believe happened. After the fix, no precautions were made (read budget constraints) to coat the tool to prevent warping cores or cavities. That explains why for awhile we had good mags and then over time they became worse and exhibited functions of the original mags.
