Sometimes the ejector lands on the left side of a magazine in such a way that it gives some pressure. (Check the ejector for a normal appearance, meaning not bent or broken, as well as normal movement.)

I'll sometimes have an occasional magazine not quick "click" into the mag well under a locked back slide (meaning no slide resistance) without a little extra pressure. There's a bit of a potential tolerance stack condition that can occur when you consider the interaction of the involved parts ... mag body, mag butt plate, window cutout in mag, mag catch body, frame cut for mag catch body. Especially when you consider the plastic butt plate and how its grooves may slip onto any particular mag body lips.

When I load a magazine I make sure I either press it up into place (when the slide is locked back), or I give a more solid push/whack (slide locked forward). I wouldn't get too "aggressive" and try to forcefully shove the mag up through the grip frame and out the ejection port when the slide is locked back, though, as its possible to exert excessive pressure up against the bottom of the ejector. I watched one guy eventually break off his ejector doing that one day.

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Ret LE Firearms inst & armorer