Short version: I worked 70 hours the week after Thanksgiving and then tried to reload toward the end of the week. I ended up with 500 rounds of 9mm just not quite powerful enough to operate the slide.
Longer war story: I was running low on 9mm and there was a GSSF Indoor League coming up. So, even though I had put in 70 hours at work and was looking at a short 45 hour, but busy week coming up, I decided to rush through 500 rounds of 9mm.
I use a Hornady powder measure with a caliper adjustment and I've developed a cheat sheet that let's me know what caliper setting gives me which powder weight. I ONLY USE IT AS A GUIDE, just to be clear. I look at my sheet and see that a setting of 3.2 should put me in the ball park for 5.0grs of Power Pistol. So I dial in 3.2, run the press about 4 times, then measure, on a scale, the actual weight. In my tiredness my brain mixed up the number 3.2 and 5.0. WOW. So, I kept dialing back the caliper until I got 3.2gr on the scale! Now that's tired. I even remember asking, but ignoring, why the caliper was off so much.
Good thing I didn't take these rounds to a match. The DNF wouldn't be bad, but the embarrassment to my ego would have really hurt. At practice I loaded up a magazine and fired the first round. It felt soft, but there was definitely a bullet hole in the target. Second shot, "CLICK". I manually ejected the round, took out the mag and checked the barrel. There was a hole in the target and the barrel was clear so I fired a second round. 2 holes in target but the slide didn't fully operate. Instantly I realized what had happened.
I considered all the options. The round appeared safe to shoot, just under powered. It was like firing .38spl wadcutter target loads. I figured between unloading them all verses firing them, it would be easier to fire them and manually cycle the slide. So I used the opportunity to fire them while manually cycling the slide. 100 left hand and 100 right hand. It was actually good practice. Slow and deliberate. I'll consume the rest over several other range sessions.
TAKE AWAY: Don't ignore anomalies in your reloading procedure. Don't reload when you're exhausted.