You open enough boxes of factory ammunition over the years, you'll find a little something that wasn't planned by the manufacturer every once in a while.
Considering the many millions of rounds produced by automated production it probably speaks quite well for the big manufacturers' quality control measures that we don't see more problems ...
I've come across mangled bullets/cases; incorrectly seated bullets; incorrectly trimmed and sized cases; primers inserted in the primer cups backwards; inert primers; squib powder charges ... and I can't remember what else at the moment. Most of the things I've listed are from major manufacturer law enforcement contract ammunition, too, although mostly within the less expensive product lines. I've heard of occasional similar occurrences even in the more expensive product lines, though.
It pays to inspect each and every round used, by visual and tactile senses, as the rounds are handled and loaded into a cylinder charge hole & speedloader or a pistol magazine, in case a visible problem can be identified before the round is used. Of course, the incorrectly trimmed and sized cartridge cases I've encountered weren't noticeable until they failed to chamber in the pistols ... during range training ... and careful inspection and comparison revealed they were out-of-spec and too long to permit chambering.
The last low-powered round I remember encountering appeared fine to the eye and finger tips ... but when it fired it was an obviously under-powered round by sound, recoil and cycling of the slide. It barely cycled the slide of my G27 ... just enough for the empty case to be barely ejected upward and out of the slide's ejection port, being thrown forward over the barrel hood and onto the slide, to 'dribble' along the top of the slide and fall off the front end of the muzzle.
I IMMEDIATELY stopped shooting and checked the pistol, and discovered the round had possessed enough power for the bullet to clear the barrel.
Haven't figured out a way to visually identify inert/hard primers, yet, either ... :banghead: Fortunately, they've only seldom occurred around me. I can't think of a calendar year when I've experienced, observed or had reported to me more than half a dozen instances over the course of a year ... but there was that one morning a few years ago when we had half a dozen different shooters experience hard/inert primers while using training ammunition from two different major manufacturers during the same qualification session. What would be the odds of that happening again???