It is a problem on a lot of ambi 21's.
The most important thing you need to do is make sure the piece that holds and releases the magazine is seated all the way into the recesses of the frame.
Look down the frame with a good light and you will see the mag release.
It has a round pin on each side that fits into a slot in the frame.
When this piece is allowed to ride up and no longer be seated all the way in it can pop out under the pressure of releasing a mag.
I use a small flat screw driver to press these pivot pins all the way down.
I've never had a problem in over 9000 rounds.
I have also gotten in the habit of pushing up on a loaded magazine before releasing it.
I also hold the release in while putting a full magazine in.
Now that it is habit it seems to work pretty good for me.
The Evil Captain Kirk
Last edited by Jim S.; 04-16-2010 at 21:07..