I awoke this Sunday morning to blissful sloth, too late to go to church. My apologies to the congregation, but I'm sure that they carried on bravely without me.
Sitting the quiet house, surfing the internet, I began thinking about 1911 magazines. Two months ago I was running my 1911 on the USPSA course and had some magazine related issues. One mag in particular would not hold the top cartridge in the magazine. During a hectic stage, I slammed the mag home and was surprised to see the top cartridge pop out of the magazine, arc through the ejection port and fall to the ground. No one saw that but me and the timer, and that mag got lost among the other mags in the bag.
So, I dragged out my 1911 and all the magazines for it, and started playing with the slide lock. Out of my sack of magazines, I identified two that would not engage the slide lock. I figured that weak springs were the problem, so I took those out to my bench.
A year or so ago I had obtained some Wilson Combat magazine springs with follower. I took apart the two offending magazines and installed the new springs and follower, then tried them in the Colt. They both held the slide lock nicely. Then I loaded the magazines. One loaded fine. The other wouldn't hold any more than three rounds without pushing the top rounds through the feed lips. A quick inspection of the feed lips revealed that they were hopelessly worn. I disassembled that magazine, looking for a maker's mark. When I took off the bumper pad, I saw holes I had drilled in the base plate to install that pad and the remnants of a Federal Stock Number. I remembered that magazine as one I had picked up 15 years ago in an Ebay lot, of standard GI magazines. I myself drilled the holes in the base plate to install the bumper pad. I put that magazine body in the vise, crushed it, and dropped it in the trash.
Changing springs in a magazine is a good idea, and that Wilson Combat kit I linked above is a good one to have. An additional benefit is because of the way the follower is made, it allows a standard 7-round magazine to hold 8 rounds. New springs are cheap, compared to new magazines, and anyone with a basic understanding of simple tools can change a spring. Now, all my remaining magazines work properly, hold the rounds securely and will engage the slide lock properly.
If you start having problems with your semi-auto pistol, look first to the magazine. That's probably where the problem lies.