Sterling 50 round magazines

[reccetrooper]

Those are Chilean PAF magazines.

The PAF is pretty much an (improved?) clone of the Sterling Mk7.

It's pretty clear that Matt Moss was unfamiliar with the Sterling Mk7 when he made his video and wrote the article.
FAMAE PAF Submachine Gun The Armourers Bench

The PAF: Chile's first indigenous submachine gun | thefirearmblog.com

FAMAE PAF - Modern Firearms

Thank you for the identification. It didn't occur to me to look at the PAF.