You got me. I thought it was a m76. 8mm and 7.62x54r are close is muzzle velocity but the 8mm I think is heavier?
I made a call. Lonnie (he died a few years back) was a class 2 ffl and made a ton of odd ball stuff. This was a one off he did. It was a 16" 7.62 x 54r but not a vepr, rpk or zastava. Maybe it was psl parts kit Frankenstein-ed together.
It had common russian style ak wood furniture and looked somewhat like yours. Your handguard, grip, stock and barrel were a little different.
I guess they weren't that close.
This would be closer but not it either. It was using a mag much closer to yours.
Attachment 445966