Abalas, all three of my mags would not lock in place. If you search the forum you will find a few references to this. The problem is the placement of the block that is spotwelded to the back of the mags relative to the sepecific dimensions of your reciever. Specifically, the mag/block do not seat far enough into the mag well to allow the locking tab to snap into place under the block. I did not realise this until I was at the range for the first time - you can imagine the words I used when I discovered that my new toy that I had waited on for months was a lowly single shot and I had to hold the mag in place with my hand to get it to feed at all
The "welfare fix" is simple - use a file to "very carefully" dress the bottom of the spot welded block. I wrapped the mag in masking tape first so I would not marr the fancy finish on the mag

and it took only 3 passes with the file to make it snap properly into place (I did a trial fit after each pass) It still takes a whack to get them to seat, but they are all fine now. Dont forget to get some oil on the fresh metal asap