That hole in the back of the Bulgarian magazine is actually so that you can tell it's fully loaded. When a mag is fully loaded to 30 rounds you will see the back of a cartridge through the hole.
I don't own any AK pattern rifles but it's cool seeing new stuff come out for them. Back in the day I really wanted a Tantal 88 but given the ammo issues I'm glad I didn't go that route.
@@PracticalWeapons I purchased 5 of the grey ones while they were on sale there not listed on there website anymore they do have the new AK103 ones though