As a now-retired military “gum plumber”, I see this fracture as not entirely surprising.

If nobody keeps tabs on the approximate round count for small arms, especially ones used for “training”; course, after course after course, things will go awry.

Detailed cleaning? Routine examination by dedicated and qualified technical personnel?

ONE small rust pit inside that “hole” and that is the beginning of a stress riser. It is likely that when someone competent takes a look at the break surfaces, there will be clues.

A worn cam pin will load the bearing surfaces of the “hole” differently and the thin webs of the hole will start to “flex” on a micro scale; NOT a good look.

To me, there seem to have been “oversight / errors” all the way up the food chain, from the shooter to the armoury management and beyond. Checking the serial numbers in and out of the armoury does not constitute a maintenance programme.

Yeah, stuff breaks, well-designed stuff breaks less catastrophically for the operator;…….. mostly.

“Training pool” equipment, be it weapons, vehicles, radios, etc, are a good place to study “human behavior”.