With 10 rounds in the mag, push downward on the case head about a 1/4 inch and then release. Does the case head pop back up and hold tight under the feed lips or does it rebound slowly and stop with rear end sag?
Then pull lightly upward on the bullet tip. Does the top round try to come up through the feed lips in the front?
There is a BIG difference between a magazine that works and magazine that works RIGHT.
Tony