Repeat after me: Slamming the magazine home should only be done by actors in Hollywood movies. In real life, whacking the bottom of the magazine to insert it into the gun usually leads to bad, bad things happening, as this thread goes to show.
Don't learn gun handling from movies and TV. Those actors have no idea what they're doing and are generally anti-gun, anyway. Learn from an NRA class or from an experienced shooter that you know. I've never met a shooter yet who wasn't willing to share his experience.
This post is not a dig against the OP. We've all screwed up, me more than most. Sometimes you have to learn the hard way. But, if you take a few seconds to think before acting, there's a pretty good chance you won't screw up as often or as bad.
Take it from one who knows: Slow down, ask questions, and learn to do things right, *especially* where firearms are involved...
Sermon over. This post was as much a reminder from me to myself as it was for anybody else. Every once in a while, it's useful to remind yourself of the basics, just so you don't start to take them for granted... Don't ya think?