Federal HST 147gr.
Chambered/cleared a handful of times over the last couple months for dry fire and range time but nothing excessive or out of the ordinary. Usually rotate the top two rounds and cycle them out every few months.
The one with the setback was the top round in the magazine, maybe from spending a few months jammed up under the stripper rail. Stripper pole? Stripper bar?
In any case (no pun intended) just a reminder to check your carry gear, my friends.