The Firearm Blog has a good post going through various changes in AK magazines during its production.
Part 1
http://www.thefirearmblog.com/blog/2016/09/17/guest-post-brief-history-kalashnikov-magazine-part-1-metal-magazines/
Part 2
http://www.thefirearmblog.com/blog/2016/09/18/guest-post-brief-history-kalashnikov-magazine-part-2-synthetic-magazines/
From: The Firearm Blog