AKM receivers are 1mm thick.
Between 20 and 19 gauge thick.
Some Yugoslavian made AKM and RPK have 1.5mm thick receivers.
Just shy of 16 gauge.
There's some Chinese stamped receivers as thick as 2mm out there!
People are operating under the impression that thicker equals stronger.
All other things being equal, that's true. But what if all other things aren't equal?
Changing the grade of steel might mean you have to make the receiver thicker to get the same strength!
I don't have the information about steel composition on issue AKM receivers, and I seriously doubt most commenters do either.
By the way, milled AK receivers are both stronger and less resilient than stamped! It's because they are more rigid and focus the firing stresses into single points. You might notice that the milled receiver was an interim solution to get the guns to the field rather than the final product.