I would concentrate more on the slide catch lever itself as was said in a previous post. It's not the magazine springs or followers that have an effect on disengaging the lever...only pushing it up on an empty mag. Once the follower engages the catch, the pressure from the recoil spring keeps it open until released onto either no magazine or one with rounds compressing the follower so as not to engage the slide lock lever again. The area on the back of the lever where it locks into the slide is probably worn so the mating surfaces aren't creating enough friction to stay latched when slamming a new mag in place. This can be further exacerbated by a weak slide lock caused by a weak magazine spring or a follower binding up. What I mean is if the follower only sort of half way engages the slide lock by not sending the lever fully into the receiving pocket on the slide then the lock up is already weak. Then if you slam a mag in, that lever is gonna pop right out the socket.

So, get a new slide stop lever, disassemble and clean your mags and lightly lube the followers then check your silde stop engagement by inserting an empty magazine and pulling back the slide slowly until it clicks into place. It should shoot up into the notch in the slide with a nice solid click. Then do the same again only this time pull the slide back as fast as you can.

If you still have problems after that then check the notch on the slide where the lever catches and maybe do what one of the other posters talked about with roughing that up just a touch with some 400 grit or something like that. I'd be willing to bet you won't have to go that far though.

Oh, and also make sure that no oil or grease is on the mating surfaces between the stop and the slide.

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