Need ID for "magazine"

This canvas magazine turned up at a surplus shop today but I have no idea what weapon it's for, can anyone enlighten me? The marking isn't readable enough anymore and the cardboard label isn't that descriptive.
The construction and materials make me think it should be quite old, and it predated any fabric MG/LMG belt-mag that I know of.

It's for a Vietnam era M60 machine gun. Holds 100rds.

Thanks, someone on facebook pointed me to the same thing. I never knew there was an early type, I just thought the type that apparently appeared in 67 was the standard since the beginning.
Quite a nice thing to find for just €5 here

It's a great score for 5 Euro.

These have never been very common to find in my experience. I have only one, and I think it is the only one I have come across in person.