The Firearm Blog has AK markings guide. If you want to identify AKs this would be a good reference.
http://www.thefirearmblog.com/blog/2014/12/04/field-guide-reading-kalashnikov-markings/
If you want to read from the source(Conflict Armament Research) here is the link
http://www.conflictarm.com/publications/
From: Conflict Armament Research via The Firearm Blog
