Originally Posted by hoc9sw

I've seen this called "auto forward", and I know that some shooters want their pistols to work this way. I was trained that it was bad, and eventually sold the only one I had that did this.

All of the above descriptions are correct. If you really slam in a mag with the slide locked open, you have a risk of shaking loose the slide stop. As I said, some shooters like this, but they are likely competitive shooters who rely on speed of a reload. I want my slide stop to hold until I slingshot the slide when I am ready to fire.

At the range, I have to insert the full mag on an open slide, because those are the rules. But I expect it to remain open.

When inserting a mag for carry, I do it on a closed slide, as there is a first cycle of chambering a round, then dropping / topping off the mag, and then inserting it again.

It sounds to me like you are hitting the mag so hard on that open slide that you are popping out the first round. That is also possible (I've done it). I've seen that when the mag springs were new, and the mag loaded to full capacity.

And a last thought - do not slingshot a slide on an empty chamber. Release the slide stop and ride the slide forward if you are not trying to chamber a round. Slides and springs are built for the force of picking off a round and pushing it into the chamber. I've gotten many various opinions about it being OK, but years with the same Army range office convinced me that it isn't, and I do baby my firearms a bit.