Heck a mouse may have crawled into the barrel why he was field dressing his fire hydrant !! House wren looking for a nesting place ?

By God,Yes

slap ammo is not designed for those type weapons, article I read said it was designed for a certain model machine gun.

I think it was a combination of things.
1. Cheap firearm.
2. Old ammo not meant for that firearm.
3. Ignorance in noticing things going wrong beforehand. With ammo behaving the way that ammo was, it should have sent up red flags.

Anytime you are dealing with military surplus ammo, you should have a heightened sense of awareness. The military does some strange things with ammo especially when it comes to "specialty ammo" . In Vietnam, they even loaded ammo with (I believe) C-4 or some other high explosive and dropped it behind enemy lines. It was a tactic to hurt morale, instill fear and doubt about their own weapons and ammo.

Years ago there was some Dominican 50bmg floating around that was extremely dangerous to fire. Whe you store ammo in a nonclimate controlled warehouse in the Caribbean, well...

Made my first zip gun and hand Canon in highschool shop class. Had to leave out the firing pin on the zip and the touch hole on the Canon. Got great grades on both. Took em home doctored em up and shot em for years