I had 2 rounds out of a box of low-bid duty ammo that stopped short of fully chambering in my pistol, keeping the slide out-of-battery.
Both rounds appeared fine to the naked eye.
It wasn't until I checked them more carefully back at the bench that I discovered both cases had been trimmed just overly long enough to prevent them from being fully chambered.
A couple of years later one of our guys pulled a round of another caliber (from another major manufacturer's contract duty loads) and experienced exactly the same problem. The case had been trimmed improperly and was just barely too long to permit proper chambering. Another
.
Fortunately, both instances were discovered on the practice range and not on the street.
I've lost count of the many ten's of thousands of both brands/calibers of these duty loads that have been fired by our folks and have been just fine.
When you think about how the big companies can run their automated equipment 24hrs a day, and turn out up to 1 million rounds in 24hrs, it's rather amazing they do as well when it comes to QC as they do.
I remember several years ago when one of the gun companies was trying to resolve some reported feeding stoppages reported by at least a couple of their customer agencies. When the company couldn't duplicate the reported problems, they eventually asked for one of the agencies to send them the duty ammo being used.
Testing at the gun company using the specific duty ammo revealed that not only were some occasional rounds exhibiting significantly reduced velocities (below required spec on the bid), but the case rim dimensions were found to be a bit out at the "generous" end of normal tolerances, and it was felt this could have contributed to the feeding problems (the case rim sliding normally up under the extractor). The gun company said they routinely test-fired with an assortment of commonly used duty ammo, but they hadn't tested that particular brand/line recently and were surprised by the tolerance variance.
Sometimes an ammo problem can come along.