I've come across a mystery magazine and to date have been unable to determine what rifle it fits. It appears to be a nose-in, rock-back 7.62x39mm mag, originally ~10 rounds but permanently pinned to 5. It's galvanized (?) steel and fairly heavy gauge at that. I've compared it with pictures of the usual suspects (Mini 30, AK, CA 858, etc.) but have come up empty. Of note, there's a notch cut out of the nose of the follower and on the rear there's a metal tab that pops up when the mag is empty, suggesting it operates a last round bolt hold-open device. The only markings are a faint star on the right side, and a "U5" (not U.S.) on the front and "U7" on the left side. The patches of light surface rust were underneath faded paper stickers that were on the sides of the mag. I peeled the stickers off looking for markings, but found none.
Any ideas?
Left
Right
Front
Back
Top
Top showing notch in follower
Bottom
"Nose in" lug
Right, showing bolt hold-open actuator
Close up of bolt hold-open actuator
Any ideas?

Left

Right

Front

Back

Top

Top showing notch in follower

Bottom

"Nose in" lug

Right, showing bolt hold-open actuator

Close up of bolt hold-open actuator