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Holy crap..that was scary..

I'm no gunsmith but someone elsewhere said it was a headspacing issue.

Sure looks like an out of battery ignition.  I don't know squat about AK mechanics and what features they may have to prevent hammer drop until the bolt if fully seated, but damn......

Could be firing out of battery or bad ammo or headspace if ammo was out of spec.

I found another thread on a different site where an AK-47 also went BOOM! 

They looked at the brass from the rounds fired prior to the one that initiated the failure.  They saw bulging and split cases that were evidence of the head spacing not set properly.  That kind of makes a case for checking your spent brass now and then to look for these conditions.

Since too little head space will probably cause the bolt to not close preventing the action from going into battery, it's more common to find excess head space whenever there's a problem in that area. 

Excess headspace can result in bulging and split cases, separation between the cartridge case and solid case head, or a pierced and/or blown-out primer.

If a fired cartridge is very tough to remove and looks like any of the above descriptions, that's a sign.

The importance of checking the headspace before continuing to shoot a rifle showing these symptoms is obvious from the OP's post.  Don't be another exploding AK YouTube video!

I thought the thread was about the importance of wearing eye and ear protection. Gloves are optional, sometimes good to have, sometimes a nuisance.

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Personally, I hate gloves. I like to feel that 'connection' with everything I am working with, but I also hate having fingerless gloves as they become pointless, as I have to switch gloves between tasks to provide protection when I need it..

When playing with your gun outside of your home, always where PPE  "No gloves No loves"