I posted this image on the Gun Nuts fanpage and asked our fans to guess what caused the malfunction. So far, no one has figured it out. The answer is jokingly called out in the post title as premature slidelockulation.
In short, this is what happens when I drop the slide too early when working on slide-lock reloads. I’ve been working on a technique called “pre-loading” the slide release. This is where, on a slide lock reload, you put your strong hand thumb on the slide release and apply minor downward pressure. The natural jarring motion of properly seating the mag jars the gun enough to drop the slide and chamber the next round. It’s more reliable than auto-forwarding, and faster than inserting the magazine and dropping the slide as two separate actions.
Here’s how this one went wrong: I was attempting to shave a few hundredths by actually consciously timing the slide drop instead of just letting it happen. Hence the term premature slidelockulation. I don’t want to the slide to go forward yet, but it does anyway. Luckily, this hardly ever happens!
The real fix to this is to work on the slide-loading technique in dry fire a lot. I’ve always done slide lock reloads as two actions: insert mag, drop slide. Combining them into one action will take some practice, but that’s what dry fire is for. It’s certainly better to have this happen in my kitchen than in a match.