Second or third round in. I'm pretty sure it was me, slim possibility that it was the ammo, but I loaded that same one later and it was fine. I've put about 250-300 rounds through it, and I usually switch mags, so they are pretty new. Up until recently, they didn't stay loaded very long, either. Yes, they are a bitch! I was actually using the loader that came with it today, since we were reloading the mags quite a few times and I also have a cut right under the edge of my thumbnail, making it hurt a little when loading the mags. Before today, I had used it just a couple times to know how to use it. I prefer to not have to rely on using the loader.