I was dryfiring with my Glock 19 using the red aluminum snap caps...and the fucking thing wouldn't cycle when I tapped & racked the slide.
Fucker was locked, so I racked harder and it opened.
The aluminum practice round's rim was ripped off.
Apparently, snap-caps have a limited life span, and 2.5 years of use has reached it.
I stripped the slide and inspected the extractor for chips, it looked like it was fine. Before I carry it again I'll shoot it, so I'll carry the Glock 26 backup with the exact same set up as Mr. G-19.
And I'm going to go buy new snap caps now.