[John Sabato]

The magazine is held in place by the top flat edge of the triangular hole in the side. It may be a couple of thousandths of a inch too low on your 2nd magazine to engage the magazine catch. I recommend that you smoke the area around the hole with a candle. Then holding the magazine catch in, insert the magazine full depth and then manipulate the mag catch a couple of times. This should let you know where the mag catch is attempting to engage the hole in the magazine. If you find that it is higher than the hole, just enlarge the hold slightly with a needle flat file to the point where the engagement was shown. Then the new mag should fit and stay retained. It may take several trial and error runs with this smoke trick to get it just right. Let us know how it works out for you...